fix(locators): findind elements by text should trim whitespace

WebDriver always trims whitespace from around the text of an element, so to be
consistent we should trim the text from button elements before doing
a by.buttonText.

Closes #903, Closes #904.

lib/clientsidescripts.js

@@ -389,7 +389,7 @@ functions.findByButtonText = function(searchText, using) {
     } else {
       elementText = element.value;
     }
-    if (elementText === searchText) {
+    if (elementText.trim() === searchText) {
       matches.push(element);
     }
   }