search: fix admin interface of collection tree
search: fix admin interface of collection tree

* Addresses issue with the modification of collection tree in the new
  admin interface that did nothing.  (closes #1860)

Signed-off-by: Petr Broz <3a04a885dc4e9da3946b4e7532bde41ba3e77029@gmail.com>

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