Upgrade JSDoc to 3.3.0-alpha 5

[shunter]

Note: this pull includes the changes from #1743 so merge that first.

This upgrades JSDoc from 3.0 to 3.3.0-alpha5, the latest available version. This version runs in Node instead of Rhino, and as a result, runs much faster.

I've build locally and deployed to

http://cesium.blob.core.windows.net/shunter-jsdoc-upgrade/index.html

so you can easily take a look.

To generate documentation, you must install NodeJS and run npm install in the Cesium directory to install JSDoc from npm. Once this goes in, I'll update the contributor's guide.

Due to our previous heavy hackery of the JSDoc source, I rewrote the template to apply our desired customizations without needing changes to JSDoc. Along the way, I changed basically everything about the HTML, including formatting changes. I'm open to revisions. I based the template on the default, but at this point we "own" the code in there now, to change as we see fit.

As per @pjcozzi, I dropped support for documenting GLSL.

Fixes #1687

[shunter]

I based some of the styling on this template : https://github.com/davidshimjs/jaguarjs-jsdoc

If you're curious what that looks like stock, I generated with that template and uploaded here:

http://cesium.blob.core.windows.net/shunter-jsdoc-upgrade/Jaguar/index.html

The main problem with this template is that because the nav bar contains all members of all classes, each and every HTML page is over 500KB (!)

Still, you may find it interesting to see another style.

[pjcozzi]

Doc build is now 47 seconds on my Mac.

[pjcozzi]

Looks good. Remember to update the Contributor's Guide. If you are up for it, it could be a good time to rewrite the Documentation Best Practices guide, which would help with #1684.