Things work now, mostly

- Added history for LiveEval

- Fixed sticky inputs in GrapherListView that didn’t disappear when
empty

- Changed EVAL button to SET button, now allows for storage in
arbitrary variable

- Refactored set variable prompt to Application (still need to merge
Application and SigmaboxAppFrame)

- Canvas so smooth, wow

- Probability distributions that didn’t work now do

- Nasty bug where Frac receiving a Number rather than a Value in the
numerator/denominator fixed