Adds join model BandParticipation with migration

[#43916603]
Seeds creates default band participations - New route for my bands

[#43916603]
Adds Band Participations controller - Leaving a band is now possible

[#43916603]
New route for requesting participation to a band

[#43916603]
Participation to a band can be requested

[#43916603]
Solves conflicts after merge

[#43916603]
Solves conflicts - Allow edit, update and destroy of band only if member admin - Authenticate user before accessing band participations controller

[#43916603]
Adds flash info when participation request pending - Filtered actions in bands views according to user status

[#43916603]
Removes date_left from band_participation

[#43916603]
Adds view members only for band admins

[#43916603]
Adds action buttons to members view

[#43916603]
Adds set_administration_rights route

[#43916603]
Adds activate route to band participations

[#43916603]
Orders participations

[#43916603]
Fixes bug when user not authenticated - Fixes bandsController tests and adds new ones

[#43916603]
Adds tests for BandParticipation Controller Model and Routes

[#43916603]
Merge pull request #9 from WilfriedDeluche/bands-participation-43916603

[Fixes #43916603] Bands participation 43916603