Add a clash delete command

[daxida]

Add a clash delete command so we can get rid of all the clashes we might dislike. It will delete the clash from our current database, and probably even blacklist it, so if in the future something like a new clash fetch all function was implemented*, it will still not appear with clash next.

Another option is just to blacklist the clash, don't delete anything, and add some blacklist checks in the random generation of clash next.

*This also makes me think. The clash fetch all will be sending something like 2k+ requests... Maybe forget about that and just ship already some clash database with the repo? A new user may find bothersome to have to manually fetch a decent bunch of clashes, were he to give the repo a try.