deposit: flag population by FormField
deposit: flag population by FormField

* Implements flag population by FormField so it accumulates certain
  flags of the fields it contains. The behaviour is configurable and
  contains the `required` flag by default.

Signed-off-by: Marco Neumann <3829486b93ec44395f0b980424bae9b6fb07b7bc@crepererum.net>

tiborsimko/invenio,inveniosoftware/invenio,tiborsimko/invenio,inveniosoftware/invenio