Refactor key extraction into single method.

This change moves all alternative key logic into a single method.
Allows message keys to be in nested in "data" or "message" object. This is to support parse.com and other providers.
Added additional keys to support Urban Airship.

fixes #147 replaces #218 and #182

Remove gcm.jar
Implement GCM Clould Messaging
Implement Token Refresh Listener
Update Android compilation instructions

Remove unnecessary didRegisterUserNotificationSettings implementation, which did break cordova-local-notifications-plugin as a side effect

Conflicting implementation of didRegisterUserNotificationSettings
prevents cordova-local-notifications-plugin from being notified of success.
emoving it fixes the problem as it was redundant (simply calls
registerForRemoteNotifications, which is called anyway from PushPlugin:init
right after registerUserNotificationSettings).

Fixes phonegap/phonegap-plugin-push/issues/183 and
katzer/cordova-plugin-local-notifications/issues/695

allow forceShow option to always notify (android only atm)

(doc) ios options

Being explicit about possible types/values on ios options: booleans can be passed as strings.
fixes #180

Bigview in inbox when only one message

Updating Readme

Updating plugin.xml

Updating support.v13 to latest version and copying the new PushConstants.java over to platforms.

Conflicts:
	src/android/com/adobe/phonegap/push/GCMIntentService.java

add error handling