Compile only *.jsx files during asset compilation

* Use a forked version of jsx.js to load JSX files with “.jsx” extension
* Rename all JSX files from “.js” to “.jsx”
* Copy non-JSX files rather than run them through the `jsx` command,
  which does unnecessary parsing
Stop gzipping until Chaos can serve compressed

The build is creating a gzipped version of the JS, but Chaos does not
handle gzipped assets. Stop doing the work until the file is used.
Merge pull request #320 from mesosphere/compile-only-jsx

Compile only JSX assets