Implement remote project deletion

[cloudhead]

It should be possible to delete a project remotely. There are two potential ways this could work:

1. Git: implement deletion via git push, eg. have a rule that if all delegates delete their default branch, the project gets removed
2. SIWE: use sign-in-with-ethereum plus an api on http-api to remotely delete a project; again, only project delegates would be allowed to do this.

[erak]

I'd vote for giving solution 1) a try, since that wouldn't require to opt-in on Ethereum. We can then implement 2) afterwards if needed.

[slack-coder]

@cloudhead this looks complete using 'rad rm'

[cloudhead]

@cloudhead this looks complete using 'rad rm'

rad rm only deletes local projects, not remote projects on seeds.