Improved Rolls

Added an improved rolls system. This addresses most of #67. Make sure:

- [x] Rolls from the main page show up in page history.
- [x] Can do an ad-hoc roll.
- [x] Can clear roll history.
- [x] Can add a general roll.
- [x] Can remove an added general roll.
- [x] Can edit an added general roll.

Right now, the outstanding things from #67 are that we have is a lack of a help page, and I haven't updated to the new version of `dice.js`. Those shouldn't block the merge of this branch.