CURRIKI-6062 : Group Profile / Masthead Image does not appear

Document.AddAttachments triggers a double save on attachments with
filesystem storage. (see XWIKI-8254).
Switched to Document.addAttachment which works fine but requires save
after.
Merge remote-tracking branch 'origin/master' into WYSIWYG
Merge pull request #7 from flaviusx/WYSIWYG

CURRIKI-6062 : Group Profile / Masthead Image does not appear and more about WYSIWYG (CURRIKI-6056).
thank you Flavius
paul