Pygments supports lots of styles, but RB currently only supports its own simple syntax highlighting. This is a first step toward supporting custom syntax highlighting. Just looking for comments on the approach.

* Add a script to generate all available pygment highlighters as static CSS files
* Add an admin field to choose the desired style
* Update templates to use a selector for the syntax highlighting

This change works well enough with light-background styles, but not with dark-background styles. We'd need to support styling the changed line backgrounds based on the colorscheme of the theme for this to work well. Also needs a drop-down for selecting styles, css to be automatically generated on install, and user-selectable themes.

http://github.com/djs/reviewboard/tree/review-1180

Unit tests pass. Tested diff fragments and review comment fragments with different pygments color schemes. Tested generating a new database.