Make theme into a consumable bundle for RTD

[agjohnson]

This makes the theme javascript modular, so the Read the Docs doesn't need to fork the code or assets internally. In particular, this:

• Makes javascript a commonjs module
• Module exports everything as public members, instead of hiding the implementation. This allows RTD to override only the necessary pieces on the instance
• Cleans up implementation to be more composable
• Creates a javascript source file and a bundle output. RTD will not use the bundled output, but others may still. It should work the same as the module does now.
• Browserify creates the bundle. This is mostly for future design -- it was left in after an original test to move dependencies into the js bundle.
• jquery, underscore, and docutil javascript is still included via the normal script tags for now.
• Installs fonts from bower now. RTD installs directly from these bower packages as well.

See readthedocs/readthedocs.org#1645 for more info on implementation there.

[gregmuellegger]

Local test successful with a local installation of rtfd.org. JS is picked up successfully, sticky nav etc works. Code also looks good.

👍 from me.

[ericholscher]

👍 -- Are we waiting on a release to do these merges with a version bump?

[agjohnson]

I'll wrap up this milestone and get a release ready. Once this is out readthedocs/readthedocs.org#1645 will need some final changes to reference the tagged release