ENYO-3025: enhance tooltip message to indicate typical top application file and the default one per default

Related JIRA: https://enyojs.atlassian.net/browse/ENYO-3025

Improve the tooltip message used in the preview tab of the project properties popup to indicate the typical name of the top application file, the name used per default and for debugging.

Enyo-DCO-1.1-Signed-off-by: Vincent HERILIER vincent.herilier@hp.com