any "clock" json parameters are now optional (#222)

This change allows to just switch back to the clock, without touching any parameters, and just display the clock as it was before. One can also specify parameters explicitly to enforce using those. Additionally "show" parameter has been removed, as it was basically unnecessary anyway. Backwards compatibility: It will work with and without providing it, as long as a "clock" json object is present.

Minimum json, to trigger clock being displayed:
```
{
    "clock": {}
}
```

Maximum (all parameters currently supported):
```
{
    "clock": {
        "fatFont": false,
        "switchAktiv": false,
        "switchSec": 5,
        "blinkAnimated": true,
        "withSeconds": false,
        "drawWeekDays": true,
        "hexColor": "#00FF00",
        "color": {
            "r": 0,
            "g": 255,
            "b": 0
        }
}
```

src/PixelIt.ino

@@ -1299,51 +1299,69 @@ void CreateFrames(JsonObject &json, int forceDuration)
         // Clock
         if (json.containsKey("clock"))
         {
-            logMessage += F("InternalClock Control, ");
-            if (json["clock"]["show"])
-            {
-                scrollTextAktivLoop = false;
-                animateBMPAktivLoop = false;
-                clockAktiv = true;
+            logMessage += F("InternalClock Control, Params: ");
+            scrollTextAktivLoop = false;
+            animateBMPAktivLoop = false;
+            clockAktiv = true;
 
-                clockCounterClock = 0;
-                clockCounterDate = 0;
+            clockCounterClock = 0;
+            clockCounterDate = 0;
 
+            bool isSwitchAktivSet = json["clock"]["switchAktiv"].is<bool>();
+            if (isSwitchAktivSet)
+            {
+                logMessage += F("clockSwitchAktiv, ");
                 clockSwitchAktiv = json["clock"]["switchAktiv"];
+            }
 
-                if (clockSwitchAktiv == true)
-                {
-                    clockSwitchSec = json["clock"]["switchSec"];
-                }
+            bool isClockSwitchSecSet = json["clock"]["switchSec"] != NULL;
+            if (clockSwitchAktiv && isClockSwitchSecSet)
+            {
+                logMessage += F("clockSwitchSec, ");
+                clockSwitchSec = json["clock"]["switchSec"];
+            }
 
+            bool isClockWithSecondsSet = json["clock"]["withSeconds"].is<bool>();
+            if (isClockWithSecondsSet)
+            {
+                logMessage += F("withSeconds, ");
                 clockWithSeconds = json["clock"]["withSeconds"];
-                if (json["clock"]["blinkAnimated"] != NULL)
-                {
-                    clockBlinkAnimated = json["clock"]["blinkAnimated"];
-                }
+            }
 
-                if (json["clock"]["fatFont"] != NULL)
-                {
-                    clockFatFont = json["clock"]["fatFont"];
-                }
+            bool isClockBlinkAnimatedSet = json["clock"]["blinkAnimated"].is<bool>();
+            if (isClockBlinkAnimatedSet)
+            {
+                logMessage += F("blinkAnimated, ");
+                clockBlinkAnimated = json["clock"]["blinkAnimated"];
+            }
 
-                if (json["clock"]["drawWeekDays"] != NULL)
-                {
-                    clockDrawWeekDays = json["clock"]["drawWeekDays"];
-                }
+            bool isFatFontSet = json["clock"]["fatFont"].is<bool>();
+            if (isFatFontSet)
+            {
+                logMessage += F("fatFont, ");
+                clockFatFont = json["clock"]["fatFont"];
+            }
 
-                if (json["clock"]["color"]["r"].as<char *>() != NULL)
-                {
-                    clockColorR = json["clock"]["color"]["r"].as<uint8_t>();
-                    clockColorG = json["clock"]["color"]["g"].as<uint8_t>();
-                    clockColorB = json["clock"]["color"]["b"].as<uint8_t>();
-                }
-                else if (json["clock"]["hexColor"].as<char *>() != NULL)
-                {
-                    ColorConverter::HexToRgb(json["clock"]["hexColor"].as<char *>(), clockColorR, clockColorG, clockColorB);
-                }
-                DrawClock(true);
+            bool isDrawWeekDaysSet = json["clock"]["drawWeekDays"].is<bool>();
+            if (isDrawWeekDaysSet)
+            {
+                logMessage += F("drawWeekDays, ");
+                clockDrawWeekDays = json["clock"]["drawWeekDays"];
+            }
+
+            if (json["clock"]["color"]["r"].as<char *>() != NULL)
+            {
+                logMessage += F("color, ");
+                clockColorR = json["clock"]["color"]["r"].as<uint8_t>();
+                clockColorG = json["clock"]["color"]["g"].as<uint8_t>();
+                clockColorB = json["clock"]["color"]["b"].as<uint8_t>();
+            }
+            else if (json["clock"]["hexColor"].as<char *>() != NULL)
+            {
+                logMessage += F("hexColor, ");
+                ColorConverter::HexToRgb(json["clock"]["hexColor"].as<char *>(), clockColorR, clockColorG, clockColorB);
             }
+            DrawClock(true);
         }
 
         if (json.containsKey("bitmap") || json.containsKey("bitmaps") || json.containsKey("bitmapAnimation") || json.containsKey("text") || json.containsKey("bar") || json.containsKey("bars"))