API: added new consts in location
SPI: removed   loadParentsForDraftContent
SPI: renamed assignmentsCount in section handler
SPI FieldType: removed onlyEmptyInstance
SPI  add deletePolicy, removed removePolicy
Merge branch 'backend_6.0' of github.com:docb22/ezpublish-kernel into backend_6.0
API: added $domainType in content info
SPI: added content id in user value

in LE the user id equals the content id but this may cause problems in NoSQL databases, when reusing there native ids which are unique over all documents/data sets.
SPI: refactored user/group/role

- added create/update structs for user/role/policy
- added role package with role handler
- refactored assignments
- moved group handelr into user handler
removed RoleUpdateStruct