New masking features

[bnmajor]

• Only apply changes to mask presentation on button press, not automatically
• Remember which image mode a mask was created in
• Remember which x-ray source was selected when the mask was created (if applicable)
• Update mask manager dialog to use a tree view instead of a table view
• Organize masks by view mode + x-ray source in tree
• Keep backwards compatibility with old mask file versions
• Automatically hide masks that were not created in the current view mode with the current x-ray source
• Collapse mask categories that do not match current x-ray source
• Allow users to skip this automatic mask hiding functionality if desired Skipping for now

Addresses #1791