Update SQL Setup

Updates to include a couple of default sessions.
UI for creating sessions

Allows a new session with a name to be created, and redirects to the
session on creation.
Add session selection to admin panel

We want to prevent the admin resetting the votes for all sessions, as
we usually only want to reset one of them.

Likewise, they will only want to see votes from that session.

Currently both DELETE events return "405: Method Not Allowed". This will
be implemented in the next change.
Implement "DELETE /session/id/vote/{id}"

Allows votes to be deleted if the session is specified.
Also removes the previous "DELETE /vote/{id}" functionality, as this is
no longer required in the front-end.