records: acl hook added to record documents.

* Add new model to represent documents attached to one or more records.

* Add pre hook to the default ACL to check user rights over the records
  that the document belong to.

* New record config variable `RECORD_DOCUMENT_VIEWRESTR_POLICY` to
  specify the access policy over documents attached to one or more
  records.

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
linkbacks: jinja base templates renaming

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
messages: jinja base templates renaming

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
oauth2server: jinja base templates renaming

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
pages: jinja base templates renaming

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
records: jinja base templates renaming

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
cloudconnector: jinja base templates renaming

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
access: file renaming

*Moves files to `admin/` directory

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
search: jinja base templates renaming

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>