ENYO-3023: Launch PhoneGap Build web help from PhoneGap Build properties tab

Related JIRA: https://enyojs.atlassian.net/browse/ENYO-3023

An icon button is used to launch the PhoneGap Build help web page in a separate tab browser from the PhoneGap Build tab of the Project Properties Popup
Currently, this button is (mis)placed on the top of the settings of PhoneGap's properties tab.
It will moved to its definitive place within https://enyojs.atlassian.net/browse/ENYO-2788 resolution which will be provided very soon.

Enyo-DCO-1.1-Signed-off-by: Vincent HERILIER vincent.herilier@hp.com