refactored for command query separation

should make things easier to test when I get round to that.
make sure people cannot rate themselves and hide save button if you aren't the organiser
First stab at scoring an event

So far it will just work out the theoretical maximum score based on
mutual ratings. It doesn't vet take into account who is going or not
because the accept / decline responses are not captured yet.
Allow invitee to response to invitation
Made scoring take into account responses, started adding a datepicker, added visual feedback when loading.