Remove BasicCommand implementation from JedisCluster

We can remove BasicCommand implementation from JedisCluster.
It's for removing confusing things.
I think no interface would be less confused than interface with always throwing error.

Please see https://github.com/xetorthio/jedis/pull/610#issuecomment-39300571 and https://github.com/xetorthio/jedis/pull/610#issuecomment-39303733 for more discussion.

Btw, I created branch "cluster-revised".
Many things have been left for improving Jedis Cluster.
But it could break backward compatibility, and we have much time to get it.
So we can merge those TODO and PRs to "cluster-revised", and merge when we're able to release 3.0.0.

Please review and discuss! Thanks!