ACL DAO level refactoring for evaluation ACLs

1) Remove the foreign key to node ID as the same column will also store evaluation IDs.
2) Add a etag column to the ACL table. Currently the etag is "borrowed" from the associated node. The etags should be extended to handle evaluations. A reasonable approach is to let ACLs handle their own etags.
3) Merge AccessControlListDAO and DBOAccessControlListDao. Don't see the need of maintaining two separate DAOs.
4) Handle the "syn" prefix correctly.