Changes to navigation to add Schedule

Users can now find a Schedule via the account menu in the top-right, and from a new home screen that non-admin users land on when logging in.

This means that users who are not an admin/owner of any squad can now log into Squaddle and easily respond to invites without having to go via WhatsApp or email.

Users who are admins can use the Schedule to respond to activities in their own squad (and/or other squads), and to use it as another route into managing their activities.