Allows users to leave a project/group
that they have been added to.
Add function to leave a namespace by url param
If the `leave` param is present on a project/group show page,
click the leave link.
+ Move 'Edit Project/Group' out of membership-related partial
+ Show the access request buttons only to logged-in users
+ Put the request access buttons out of in a more visible button
+ Improve the copy in the #remove_member_message helper
Signed-off-by: Rémy Coutable <remy@rymai.me>