Modify seed for all gigs not being on the same day

[#50838221]
Add scope Upcoming to Gig - Add scope by_search to Gig - Use of upcoming scope depending on current_user role

[#50838221]
Add button in gig view - I18n

[#50838221]
Add unit test for Upcoming Gigs

[#50838221]
Merge pull request #19 from WilfriedDeluche/concerts-date-scope-50838221

[Fixes #50838221] Concerts date scope 50838221