Event to Calendar

Using Phonegap native API, provide a button to add an Event to the native calendar of the phone.

TESTS:
* iOS 7: OK (doesn't let you select which calendar the event is added to)
* Nexus S (Android 4.1.2): works OK but going back to the application does not work, seems to be linked to the "Success" callback being called when the application is called (because an Intent has been fired when attempting to add the event)

TODO:
* try to provide a fallback using iCal (see https://github.com/ox-it/moxie-js-client/pull/71)

NOTES:
* latest version of the plugin is for Phonegap 3.0, we might want to investigate moving to it