Protecting Images from being removed from the library

Is your feature request related to a problem? Please describe.
I mainly do bird photography, which means I typically come home with several hundred — sometimes over a thousand — images per outing. Keeping them all is obviously not an option, so after importing into darktable I go through an extensive culling process where each image is either kept or rejected. Once that's done, I apply the "rejected only" filter and delete those images in bulk. I use the 'delete to system trash' option to keep my folders organised.

Every now and then, during culling, I come across a shot I absolutely don't want to lose — a real keeper. But some time to time I accidentally remove the images from the catalog. Of course this is stupidity from my side, but it happens.

Currently, I flag those with a high star rating as a kind of mental safeguard, but star ratings are really meant for quality grading, not for protecting files.

Describe the solution you'd like
I would like that I can flag an image as 'locked'. And that darktable prevents me from deleting the image unless I unlock the images first. This can be as simple as disabling the 'delete' and 'remove' buttons 'actions on selection' module in the lighttbale.

I would be even more awesome if this solution could be made compatible with the 'image protecting' features Nikon and Canon have in their camera's. That is: upon import that meta-data is read and if 'lock the image' is in the meta-data, that the image is automatically locked in the darktable. But this feature is just added niceness and absolute no must.

Alternatives
Currently I use - as described - I use a star rating, or I have used marking the image with a color tag, but this of course doesn't prevent actual deletion. It is pure a mental note.

Additional context
See also the discussion: on pixl.us. The discussion also mention the ability to freeze and image from editing. That also would be nice! But maybe that is a different features request. Although this can maybe implemented in one go by using a enum rather then a boolean.

Start with the lighttable's "actions on selection" module, which the issue identifies as the place where delete and remove actions could be disabled. Read the linked pixls.us discussion for the proposed locking and editing-freeze behavior. Done means a locked image cannot be deleted or removed until it is unlocked; camera metadata import is optional scope.