ipfs name resolve '-k' option unecessary

We should just be able to resolve named keys by doing ipfs name resolve keyname. Since named keys cannot contain slashes, we can disambiguate them from hashes by an optional /ipns/ prefix on hash keys.

ipfs key gen foobar
ipfs name resolve foobar # should work
ipfs name resolve QmBeepBoop # should check if we have a key named QmBeepBoop, then try to resolve a hash key
ipfs name resolve /ipns/QmBeepBoop # definitely a hash key, don't check for named keys