ENYO-3045: change the emplacement of "Phonegap.ProjectProperties.KeySelector" from ProjectProperties.js to PhonegapUIRows.js.

So, the row "Signing Key" is instanciated in the when the panel "Phonegap Build" is created an not at each opening of the Pop-up "ProjectProperties".
ENYO-3045: when the Phonegap build panel is displayed, the default signing key of each plateform is selected.

A modifications are also done to improve the usability of this component :
* The message "Loading signing keys ..." is displayed while the Ajax request to get the user data is pending
* The inputs "key password" & "storage key password" and the button "save" are shown only when a signing key is selected.
* If the Ares user is authentified with a Phonegap account "A" > change to the Phonegap account "B" > comeback to the account "A" . Then the existing signing keys are not recreated.
* If the Ares user is authentified with a Phonegap account "A" which contains a set of signing keys for a given platform & switch to the Phonegap account "B" which contain also a set of signing keys in the same platform. Then the picker contains only the signing keys of the account "B".
Merge branches 'ENYO-3045' and 'master' of github.com:enyojs/ares-project into ENYO-3045
Merge branch 'master' of github.com:enyojs/ares-project into ENYO-3045
Merge pull request #522 from enyojs/ENYO-3045

ENYO-3045: Pre-select the platform's signing key in the UI Phonegap Build as defined in "project.json".