Allow the plugin to know when the app is no longer in foreground so that it may receive push notifications

Added clobbers for PushNotification

JSON fix

Callback now invoked

Android : getString should be extras.getString

added foreground boolean

Added getString method to setContentTitle and setTicker

Enable syntax highlighting for code examples in readme file

ContentTitle and Ticker can now be set from the GCM server via the
"title" field in the "data" parameter (appName is no longer hard coded).

Eliminate need for GET_TASKS permission

Fixes Cordova error when trying to open the app from the notification bar

Added a missing comma after errorHandler

* Don't check if we are in the foreground - that happens anyway in the
sendExtras() method (https://github.com/phonegap-build/PushPlugin/blob/master/src/android/com/plugin/gcm/PushPlugin.java#L111)
* Only display a message if the message has text to be displayed

Fixes #52 and undoes #3

Use & instead of your large and error prone if statements

Fix typo: successCallback should be errorCallback

Finalize pre-3.0.0 plugin fixes

plugin submission requires a version bump even if plugin was previously
deleted (bug?)