Check for field name duplicity on creation; refs #642

Also remove repetition texts on separators
Fix membership selection
Membership was checked against logged in user, and not displayed member; fixes #725
Hide days for inactive late members; fixes #716
Staff members cannot change their own informations; fixes #726
No error was displayed on remove member error

Display a specific message if member still hae dependencies (on mailings for example); fixes #680
Bump version
Update changelog
Update translations
Merge branch 'release/0.7.6' into develop