Fixed Export Bug

The default save type is PNG. If no type is written by the user it is
saved to the correct filetype. If the file type given by the user
differs from the one selected, it correctly saves to the user-specified
file type (although we could change this so if you selected PNG image
and saved as "test.jpg" that it would save as "test.jpg.png" and still
be a PNG image.
Fixed Resize Component Bug, and Filter Bug

Resize components could be clicked from further away than intended.

If a filter was called on a layer that had already been filtered a
NullPointerException would occur when trying to access the first filter
history object's actionImage.
Set minimum resize value for DrawingArea/Easel

Also added an Oval Shape, and made the background of the easel more gray
so that the GUI was easier to look at.