Calc

- Moved some things around to make them more clear (at least in my opinion).

- Made it so that answers are specified using block xml instead of Expressions (to make level building easier).

- Created level builder support.

Of these things, the level builder stuff is probably that which could most use review.
I think this will affect Multi and Match levels -- we may want to leave those as a single edit page (vs. create on separate screen).