Add csslint task

Because of the current parser-lib issues with @-moz-document and IE
expressions this task isn't included as part of the default pipeline.
When run, it should use the `--force` flag till this issues are patched.
Add base64 encoding of CSS

Caught issue where the images for the intranet theme need to be copied
from the GCWU theme
Add Bundler setup for repeatable Gem installs
Update Travis build to use node