Implement revoking someone from a group
Update the revoke button

When an admin revoke someone, it revokes it membership, so there is no
need to display the current role of the user being revoked.
Small layout change
pep8 fix
Save account activity when joining a new group
Register account activity when user is promoted within a group
Register account activity when the user's role is downgraded in a group
Register account activity when the user is removed from a group
Register account activity when the user revokes itself from a group
Fix the int used for the activity log
Register account activity when an user applies or joins a group
Do not show the collapsible panel if there is nothing to show in it
Adjust the int for the activity log per @laxathom advice
The button is the link rather than the link in the button
Update initdb script to an administrative commande-line tool.
Merge branch 'fas3_pingou' into FAS_3.0
Only display approved group from the list "involment".