Delete unused legacy templates.
Move disqus config to slingsby/settings.py.

This is part of not having config values strewn about all over the code.

Added a config context processor where config values needed in client-side
code can be added. This is saved to the client-side `slingsby.config`
object.
Remove references to app engine in html comment to devs.
Make sure listeners and binds are done asap in musikk.js
Optimize and compress static graphics.

Use grunt-contrib-imagemin for this.

In the process, move all originals into a gfx/originals directory so
that we can exclude them from the optimization.