Consolidate the HTML5 and JavaScript directories into a single HTML directory

All implementations utilizing HTML will become subdirectories and use
appropriate symlinks to pull in the HTML + JS. This is why everything
but index.html that is needed for deployment is in a single assets
directory: to make symlinking easier.
Move App Engine code under HTML
Stop tracking the cache.manifest file
Use a local copy of the Source Sans Pro

Deals with future download issues stemming from Chrome app.
Don't track build.ninja
Move all JS out of index.html to meet CSP requirements
Generate a Ninja build file to copy necessary files and generate a zipfile
Support startup.js
Add Content Security Policy support

As specified for Chrome apps.

Closes #23
Merge branch 'chrome_app_v2'