Save button now behaves correctly for filter changes.

Basically, save the original filter from the file's XMP.
Compare the current filter against original one to decide whether or not the
file has been modified and needed to be saved.

At the same time, make sure we don't save "None" filter in the ImagePreset.

bug:9468909

Change-Id: I5b86ab95556b6b010367c9577b02c0bb42ffb824