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
```