tidy up css and font files
    
    this commit does some general tidyup of how we handle some
    of the CSS and font files.
    
    First, the two fonts we use, open sans and fontawesome are now
    set up to be pulled down from the central copies we have hosted
    on apps.fp.org/global. Note that due to CORS restrictions, this
    means these fonts will work on prod, but not when testing locally.
    If you install the fonts locally on the system you are looking at
    the test site at, it will use the fonts. Details on this have been
    added to the dev documentation.
    
    Second, we remove the cantarell and comfortaa fonts in the repo,
    as these were not being used. We also delete the style-patternlab.css
    file that was not being used either.