Implement HasBeenSaved tracking

[tannerhelland]

Implement HasBeenSaved tracking

[tannerhelland]

.HasBeenSaved is now implemented as part of the pdImage class. The save button(s) on the main form are enabled/disabled based on that property. Per convention, the save button is disabled on image load (if the image was loaded from the hard drive - imported images obviously leave the save button enabled). The save button is disabled after a save has just been performed. Undo/Redo also effect the save button state - if Undo is used to return to the image's original state, the save button is once again disabled (for images on the hard disk). Redo re-enables the save option.

One odd case is if the user performs a series of actions on an image, then saves the image. Other software programs disable the Undo button at this point, but I don't like that - it may be useful to save an image, then Undo to a previous state and save, or start working from that point. In that case, the save button will be disabled on the initial save, but if the user clicks "Undo" and then "Redo," the save button will be re-enabled. I consider this a feature, not a bug.

I'm leaving this open because I still need to prompt the user re: unsaved images at program or image close, and that requires some INI work (so the user can turn off prompting).

[tannerhelland]

Fully implemented as of 78047db