mention cookie requirement, resolves mediathekview#168

The main page displays a error box “your browser is not supported or JavaScript
is disabled” even though the root cause is that Cookies are disabled. This is
very confusing. This change mentions Cookies in the message as well. Evidently,
the best solution would be not to require cookies at all.

client/index.html

@@ -106,7 +106,7 @@
 
       <div id="browserWarning" class="showafter1s" style="border: 3px solid red; padding: 10px; margin: 15px">
         <span><a target="_blank" href="https://github.com/mediathekview/mediathekviewweb/issues/8">Dein Browser wird
-            nicht unterstützt</a> oder Javascript ist deaktiviert</span>
+            nicht unterstützt</a> oder Cookies oder Javascript ist/sind deaktiviert.</span>
       </div>
 
       <div id="main-view">