[WIP] Implement caching ObjectState handler

JIRA: https://jira.ez.no/browse/EZP-23462

TODO:
- [ ] Unit tests
- [ ] Possibly cache object state info by content?
If you look to the other handlers there is no use of with and without ´s´, there is always the singular form with things like 'all' as second key to store id maps.

Same goes for use of 'objectstates' below.