Adds a cider-clojurec-repl-type-override variable to allow overriding the default behavior of sending CLJC evals to both CLJ and CLJS.

Also includes a cider-set-clojurec-repl-type-override function to prompt the user to set this variable local to the buffer

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If you're just starting out to hack on CIDER you might find this section of its
manual extremely useful.