Defer choice delete until Save

Changes
-------
- Added docstrings in the endpoint explaining what data is expected
- Removed markup for the delete choice confirmer from the template
- Removed markup that cued the JavaScript to pop up the delete choice
 confirmer
- Added markup for a trash div to hold pending deletes
- Removed a JavaScript TODO for the Save Confirmer in favor of an issue,
 OpenTreeMap/otm-addons#1493
- Replaced JavaScript code dealing with the confirmer with code
 to stage deletions to a trash div
- Related JavaScript changes for the content of the Save Confirmer,
 and fixing the dom up after Save or Cancel

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Connects to OpenTreeMap/otm-addons#1482

Author: RobinIsTheBird