Cache only 200 results in /assets/*.
Cache all assets.
Move all assets to CDN.

Note that while rebasing this commit, I (@seanlinsley) added
a good deal of extra changes since we were still using
the static "/assets/foo" URL in a lot of other places.
Fold chosen.css and reset.css into gittip.scss.
remove unused assets
version all assets

This doesn't version the old widgets because people may still be using
them. (ref: #1767) Except... the first widget refers to an old version
of jQuery that we haven't provided in a long time :-/

This commit also fixes reset.css and chosen.css to correctly load.
remove now-unused `asset_url`

and start using that name for `asset_version_url`
use `asset_url` for elsewhere icons
turn `get_avatar_url` into a Jinja macro

that way it has access to the website object by default
Bump version to 12.4.0
Bump version to 12.4.0-dev
...that produces a valid url
Bump version to 12.4.1
Bump version to 12.4.1-dev
fix cache_static for CDN requests

our asset URL in production is the full path to MaxCDN, so this code
would never work.
Bump version to 12.4.2
Bump version to 12.4.2-dev
percent-encode an image URL in the README
Switch to a new Twitter dev app

We killed the old one during #2239.
Fix GitHub dev app; #2239