Add new methods for assigning and removing groups to/from resource

- add method removeGroupsFromResource
- add method assignGroupToResource
- add these method also to RPC
- methods are only cycles through existing methods removeGroupFromResource and assignGroupToResource in BlImpl
Merge pull request #150 from stavamichal/Add-methods-assigned/delete-groups-to/from-resource

Add new methods for assigning and removing groups to/from resource