Duplicates workflow

[Webreaper]

Now that the hashes are created (see #78), need to thrash out the workflow for managing duplicates. High-level:

1. Duplicate page lists images that have duplicates (by image data). Show one image on the left, and a list of duplicates thumbnails that match on the right.
2. Checkbox to include "visually similar" duplicates
3. For each duplicate on the right, provide a checkbox to 'action' the duplicate. Note that once n-1 checkboxes are checked, the remaining checkbox (which is deemed the 'original / to keep' image) should disable itself.
4. Checked duplicates can then be actioned by a button at the bottom of the screen. Options for processing are:
   • Delete the duplicate images (BIG warning)
   • Move to a new folder (generic duplicates folder? Or let the user choose?)
   • Images tagged with keyword (default: duplicate)
5. Perhaps have a bulk mode to auto-select the right images. For example: "Keep oldest", which will check the checkboxes of all but the most recent (date taken, or date modified).
6. If the auto-selection of the images to keep is incorrect, the user could switch them by drag/dropping another image from the right-hand-side onto the main thumbnail.

Will look something like this. Control can also be used for person/face tagging workflow, per #227

Anything else?