Added assign/unassign loanofficer to a group and update api docs

Hi Keith,

Updates are as follow

* Added new services for assign/unassign loan officer to a group
* Updated API docs for all Group related services

Pending tasks on *Group*
* Added maker/checker workflow
* Update responses as per latest standard (Send basic data back)
* Change /groups/{groupid}/command/assign_loanofficer & /groups/{groupid}/command/unassign_loanofficer as query parameter

Thanks
Nayan Ambali