Improve Masking

[bnmajor]

• Offer on-hover feedback that indicates which mask is being used in a current area
• Use "apply" instead of immediate changes to prevent excess re-rendering
• Make sure masks in one view are disabled when switching view
  • Masks created in XRS1 are disabled/turned off when switching to XRS2
  • Masks created in raw are exempt regardless of which x-ray source they belong to
• Move from table view to tree view for mask manager dialog
  • Masks should be nested under the view they we created in (raw, polar, polar/XRS1, polar/XRS2, etc.)

[bnmajor]

@psavery @saransh13 Please feel free to add to this if more items come up!