[DS-1519] Workflow and submission process selection based on community hierarchy

The main goal of this patch is to be able to define a submission process, a form definition, or a workflow process, based also on community's handles, allowing subcommunities and collections to inherit those definitions.
This patch changes the lookup process in order to check for collection's handle first, and then for its parent community's handle if the first didn't match any definition. This is the same for form definitions (input-forms.xml), submission processes (item-submission.xml) and workflow processes (workflow.xml).
According to this, it was also modified the attribute's name used to bound a definition to a handle: before it was "collection" or "collection-handle", now it's just "handle" (old attribute names are still supported for compatibility). This would need to be documented properly.

I'd like to hear your thoughts on this