Removed unnecessary IIFE.

Gets rid of the unused `init` assignment.
Added in undo/redo keyboard shortcuts.

- Adds in keymaster by @madrobby to handle shortcuts.
- Introduced a method that will ensure an element is enabled before
  triggering a click, used for filtering undo/redo eligibility.
- Added keybinding aliases ctrl+z/ctrl+y for undo/redo.
Added tooltips for undo/redo.
Merge pull request #1 from tbranyen/add-shortcuts

Add shortcuts