Soft delete ads for a short period (and use them to detect dups)

[deivid-rodriguez]

Some users skip the "5 days republication restriction" by deleting the ad and republishing another one with the same content.

Maybe we can soft-delete ads for one week (and then hard-delete them after that) and use that soft-deleted copy to detect this situation. We might want to add a text similarity measure with a very high threshold (in case they change something very small).

This could also be useful for detecting (quasi-)exact duplicates of spam ads and forbid its publication.

@andreslucena @iokese @enetron sounds like a good idea?