Name REPL buffers with `*clojure` prefix

Emacs convention is to name REPL buffers with language prefix and *cider-repl` prefix doesn't play well in switching buffers because of the redundancy with other buffers.

`cider` is never unique as a plethora of cider buffers can be floating around. `repl` is not unique either.`*nrepl-messages*`, `*nrepl-server<x>*`, `nrepl-client.el` are always there for me. Beside that, I have plenty of Gnus buffers that contain `replied` in them. So it's pretty difficult to switch to REPL buffers even with IDO. 

On the other hand `clojure` is an unique name and no confusion with other packages is likely to occur in the future.