Theme optimization

Merges @glamrock's theme-optimization branch from the archived luci-theme-commotion repo, with some adjustments for the recent repo merge and theme structure changes.

This pull request is intended to remove unused selectors, not fix outstanding style change requests.

To test, flash one node with master branch and one with theme-optimization. View pages in Firefox, Chrome, IE, and Safari and make sure the versions look the same. There may be minor variations, but they should be pretty close.