Add Gemfile for backend folder

Not super important.
Add asset pipeline gem

It'll be hard to explain in this commit, but this will allow us to
minify assets pretty simply. Check out the gem:

https://github.com/kalasjocke/sinatra-asset-pipeline
Unify all our JS into one file
Remove some old bootstrap and combine CSS into one
Remove vendored stuff we get from CDNs

These assets are currently loaded from CDNs, so we don't need a copy in
our repo. If we want to bring them back, we should use something like
Bower to manage them.
Teach git to ignore the .sass-cache directory
Eliminate the starlike favicon
Add Rakefile like I was told to

This guy says it, it must be true:

https://github.com/kalasjocke/sinatra-asset-pipeline
Add rake to Gemfile
Update assets_precompile array to be correct
Ignore compiled assets directory
Cache API responses

Since they can't change more often than the underlying data, we can
cache them indefinitely. They are invalidated by a record existing in
the `imports` table with a higher timestamp.
Merge pull request #99 from ted27/asset_pipeline

Asset minification and cleanup