[#ENYO-1712] implement phonegap build using signing keys

This is hopefully the last pull request of this marathon task... 

* ENYO-1712: PhoneGap Build integration, with signing keys passwords
* ENYO-1712: add popup-links to manage PhoneGap account & apps.
* ENYO-1712: phonegap: invalidate token when switching accounts
* ENYO-1712: working keys load/store across platforms
* ENYO-1712: PhoneGap.ProjectProperties - use static members appropriately
* ENYO-1712: Display Keystore password input form for Android

Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>