Only venue managers can create gigs - Gig is managed by is own venue managers only

[#50719171]
Adds rights to band member to create gigs with one of their bands as main_act in whichever venue - Refacto as well

[#50719171]
Adds validation on gig venue and main act depending on current user role

[#50719171]
Adds test for GigsController - but some actions missing

[#50719171]
Fixed tests bug to remove venues and bands after testing uploaders

[#50719171]
Merge pull request #18 from WilfriedDeluche/gigs-access-rights-50719171

[Fixes #50719171] Gigs access rights 50719171