Merge pull request #8 from jcard/master

Undo and Redo buttons grey out if there's nothing to undo or redo
Buttons highlight when clicked
Icons

Added icons for Select, Class, and Agg. More to come later!
Icons Cont.

Finished icons. Also went back and removed the anti-aliasing from the
original icons. I rendered them that way by mistake.
DEEP CLEAN

Removed unused imports, unused variables, irrelevant comments, the two
random extra 'main()' methods that were in random classes, and
CTRL+SHIFT+F'd every file!. Clean code is clean. Still going need more
work but great start.
Fixed a few bugs with undo and redo
Selector button is selected by default
Can export as image
Added file filtering to save/save as/open/export as image