Groups saved, admins created, members invited 55%

Now when a user creates a group, they are made the admin of the group
(so that in the future they may ban or remove members), and the group is
update with an admin ID and the first member (also the admin).

Each user added to the group will also receive an invitation to join the
group, which they may accept, reject or block. The next step will be to
make a function that allows this.

Finally, notifications are now implemented, so a user will see when they
have been invited to a group. 55% complete