Add custom button with states for image

[uliwitness]

This could just take the form of "pressedIcon" etc. properties on regular button, and then you switch them to rectangular and turn border & fill transparent and the icons auto-switch.

Alternately, we could have some way to "clone" a group of draw graphics and just permit the user to hide/show sub-elements (or even groups) of the main group from mouseDown handlers to perform custom mouse tracking & drawing.

[uliwitness]

"Starter bug" refers to the less complex version that just has properties that let you specify different icons to use for disabled/inactive/pressed/normal. Make sure this is consistent with the names chosen for #62.