Adds managership scaffold

[#46971655]
Adds 3 default venue managers to seed - Each default venue has a manager

[#46971655]
Adds restrictions on band creation

[#46971655]
Adds restrictions to venues controller - Managers is created when Venue is created

[#46971655]
Band Participation is created along with Band creation

[#46971655]
Fixes bug when too many requests to Gmaps - Adds virtual attribute skip_geocoding which is used in seed

[#46971655]
Fixes all tests and adds some new ones for managership

[#46971655]
Merge pull request #11 from WilfriedDeluche/managership-46971655

[Fixes #46971655] Managership 46971655