Basic Group Crud

[rjarvi]

Implement basic CRUD operations (endpoints + frontend)

• Create group
• Join group (ignore starting location, see Add location functionality to users and groups #10)
• leave group
• delete group (leader only)
• squad code implementation - share join code

[vidunikankan]

• group backend setup general
• createGroup screen
• groupCreateSuccess screen
• groupCreate backend + POST endpoint
• group leader information automatically saved with group information
• allGroups endpoint
• groups display on homepage
• delete group (group leader)
• add groupUser array to group model
• join group (updateGroup endpoint + calling & filtering allGroups endpoint)
• leave group (call updateGroup)