Remove dependence on Web UI from css lib. Unfortunately we still have a
dependence on html5lib to run the test suite.

Review URL: https://chromiumcodereview.appspot.com//12278022
Update csslib version

Review URL: https://chromiumcodereview.appspot.com//12283023
update badge to drone.io
Update on csslib for 0.3.7+5

Review URL: https://chromiumcodereview.appspot.com//12303029
Bump csslib pub version too

Review URL: https://chromiumcodereview.appspot.com//12298043
More cleanup in csslib

Review URL: https://chromiumcodereview.appspot.com//12304035
Merge