Handle the situation where the username did not map to any user
Add a 'Create an account' link on the login page
Add an unique constraint on the GroupMembership table

This constraint makes the combination user_id/group_id unique over the
whole table.
This makes sure a specific user cannot be member of a specific group
multiple times
No need for JOIN when WHERE is sufficient
Simplify the syntax a little
Drop the OnClick syntax
Fix how is found the membership of the authenticated user
Add a new end-point where people can ask to join a group
Make the `join` button in the group details page work with the new endpoint
Present the pending Members on the details group page
Simple typo fix in a variable name
Include the username in the link instead of just the avatar
Use username instead of the user id for the link to the user's detail page
Use user's username instead of the user's identifier and fix indentation a little
More update to use the user's username instead of the user's identifier

Adjust the indentation a little more as well
Only show the person's introduction if there is one
Allow the edit_profile to rely either on the username or the user identifier
Remove debug code and prevent the user from trying to join multiple times the same group
Inform user trying to join of their status when they already have a membership
Activate the admin account user when initializing the DB