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>