ENYO-3090: Allow to remove a project template source from ares configuration with "type" set to "null"

Enyo-DCO-1.1-Signed-off-by: Yves Del Medico <yves.del-medico@hp.com>
Merge pull request #541 from enyojs/ENYO-3090

ENYO-3090: Allow to remove a project template source from ares configuration with "type" set to "null"