Use upstream clojure-mode.js

[cldwalker]

Our clojure mode is forked and different from the official one. As seen from our clojure-mode.js history, our fork has a few differences from the upstream one. Specifically, these changes:

• [x] https://github.com/LightTable/Clojure/commit/44884869fe4df2922d1b3d9432805b591d49b423 - covered by CodeMirror https://github.com/CodeMirror/CodeMirror/commit/1a1e6a7e7156e2acf653192dd0d80b14f8c7578f
• [x] https://github.com/LightTable/Clojure/commit/0b104acedb8ef4dedb1ba2eb23001172fa9a948b - Opened https://github.com/codemirror/CodeMirror/pull/3776
• [x] https://github.com/LightTable/Clojure/commit/bcac085f3556cb296134b75e5dbd13913af6c1f4 - Opened https://github.com/codemirror/CodeMirror/pull/3774
• [x] These three mime declarations are unique to us. We only need the clojurescript one. - Opened https://github.com/codemirror/CodeMirror/pull/3775

We should understand these changes and decide either to ignore them or discuss and submit upstream. Once our desired upstream changes are merged we can just curl the CodeMirror file directly into our repository.