Improve error reporting in MongoMapper
wip: questions-settings
added $model->exists($id) method on MapperModel
(cherry picked from commit 053c4c719a80863d99c7bf2170874cf12e21eb74)
ProjectModel test fixes for Realm.
Fix JsonEncoder re encoding of reference list.
wip: session variables for rights.
Fix json decoder for decode of ReferenceList
Implement rights as angular service.

* sessionService now has method hasRight and constant (functions) for realm, domain, and operation.
* implemented rights for projects page.
wip: project rights