core: ObjectIdentityChecker cleanup

- Change the type of mPermitted from List to Set and of mDictionary from
  Map<Enum<?>, List<String>> to Map<Enum<?>, Set<String>> which are
  more appropriate because each value in those lists should appear at
  most once (instead of verifying when adding something, that it's not
  in the list already)
- Rename ObjectIdentityChecker's members such that they'll conform the
  standard naming convention in java (instead of starting with 'm')
- Replace statements of the following structure:
  <type> <field_name> = null;
  if ((<field_name = <value> ==/!= null ...)
  with statements of the following strcture which is more readable:
  <type> <field_name> = <value>;
  if (<field_name> ==/!= null ...)

Change-Id: I7845cb876f0edcfd1a9c58a06ff443175295c554
Signed-off-by: Arik Hadas <ahadas@redhat.com>