feat(dice): Basic rolls and modifiers.

More tests are needed.

There's a lot of work yet to be done before some new
features can be included. For starters, this controller
does too much. It should split into several smaller units,
namely, a constant for roll types, modifiers, and regexes.
A new controller for handling just rolls, which includes
meta-data about the roll (any rerolls, success details, etc.).
Finally, a roll printer should report these in a table that
populates as you continue rolling.

Future features:

Old rolls are saved to local storage.
Stashing and popping roll sets from local storage.
Old rolls populate into a type-ahead for auto-complete.
A table displays roll input, meta-data, and results.