Removed the Cordova.addConstructor wrapper, replaced DroidGap

Cordova.addConstructor was removed
See http://stackoverflow.com/questions/10587398/cordova-custom-plugin-structure-w-o-callbacks and http://stackoverflow.com/questions/16082637/alternative-to-cordova-addconstructor

DroidGap was replaced with CordovaActivity
See apache/cordova-android@48b8c69