Add in-UI support for mask images

[CollinHeist]

• Mask images should be visible within the UI from a submenu of a source image. This should connect to Add optional connection to a background removal tool #481 in which an image can be sent to a background removal tool, and the mask image should be previewed/uploaded to TCM.
• Image should also be edited / cropped
  • Definitely the ability to hand draw crop lines (e.g. lasso select tool)
  • Possibly a full-image cropping mechanism