Groups api

# Approvals Required:
- [ ] @NahimNasser (Nahim)


# Stories
1. [MOB- 1120] As a developer I want to support an API end point that proxies creating a game group on Facebook. 
2. [MOB- 1182] As a developer I want to support an API endpoint for adding users to a FB group. 





# Implementation of all API endpoints that relate to Facebook groups functionality. 


1. An API to create new course groups

    **Example request**:
        POST /api/mobile/v0.5/groups/create
        Parameters:  name : string, 
                    description : string, 
                    privacy : open/closed

    **Response Values**
        {"group-id": group_id}

2.API to invite members to a group

    **Example request**:
        POST /groups/invite/<group-id>/members
        Parameters: members : int,int,int... 
        **Response Values**
        {"success" : "true"}        If adding all the member succeeded.
    
        {"error" : "error message", "member" : "id"}
                                    If one of the members provided can't be added to the group.The error message pertains to the first member that couldn't be added. Note that either all the members are added or none at all. 
                                    
3.API to delete a group

        **Example request**:
        DELETE /groups/<group-id>

        **Response Values**
        {"success" : "true"}

4.API to remove a member from a group 

        **Example request**:
        DELETE /remove/<group-id>/member/<member-id>

        **Response Values**
        {"success" : "true"}