Publish only to selected repos

[laughedelic]

Adds publishOnlyTo task, which takes one or resolvers and publishes only to them. Allowed resolvers are those defined in the publishTo chain.

TODO:

• [x] complete resolvers from the publishTo chain
• [x] actually run publishing
• [x] add tests for it
• [ ] ~~think of renaming (probably even a command with the publish name if it doesn't cause problems)~~

[laughedelic]

• [ ] Resolver names with spaces?