[Improvement] Add option to delete bookmarks after download

[Wikinaut]

As Twitter only allows you to download ~800 bookmarks *), it appears to be important to be able to delete each bookmark after it and its assets have been locally downloaded.

I suggest an implementation - perhaps with an option which affects only deleting bookmarks of the most recent n days which could be set to -1 or all to delete all bookmarks after download.

*) https://developer.twitter.com/en/docs/twitter-api/tweets/bookmarks/introduction