ENYO-2723: the iconButton related to a relative path in projectProperties indicates if the path is valid or not (top file path currently)

Related JIRA: https://enyojs.atlassian.net/browse/ENYO-2723

* In any specific project related properties, the "Top File" relative path for the "Preview" has an "iconButton" to trigger its update. This button now indicates if the path is valid or not (in order to avoid path issues after having rename a file or a folder in the file manager).
* Code has been made to better integrate icons/splashscreens path checking for PhoneGap properties (cf. https://enyojs.atlassian.net/browse/ENYO-2512)
* Continuous improvement: 
 * Image licence: https://enyojs.atlassian.net/browse/ENYO-2726
* Old resource definition given (name for icons, files...) are considered as not valid until an update mecanism will be added to project properties (cf. https://enyojs.atlassian.net/browse/ENYO-2761)

Checked on Windows 7 : Chrome

Enyo-DCO-1.1-Signed-off-by: Vincent HERILIER vincent.herilier@hp.com