Remove unused CSS from everypolitician-docs and viewer-sinatra

[chrismytton]

The documentation now lives in a separate repo from viewer-sinatra. Therefore there is now duplicated CSS in both repos.

It would be good to remove any unused CSS in each repo.

[chrismytton]

Useful links:

• https://github.com/peterbe/mincss
• http://blog.gospodarets.com/finding_unused_scss_variables/