Seperated styles

Followup of Pull Requests #1 and #2. This one was done from scratch to make sure all changes since other pull-reqs' updates are included.

- Seperate css rules based on ```@group``` hints to dedicated, already existing files
  and leave only Sunburst design-specific styles in public.css. This way, your
  own theme can depend on Sunburst but exclude the public.css file, which leads
  to way less style overrides while still having a Plone-like User interface
  (edit-bars, tables, forms, etc). Fixes pull-requests #1 and #2. Upgrade step
  included (upgrade_step_2_3).
  [thet, TH-code]

- Move workflow color definition for state "published" to public.css. The
  "published" color definition is propably something to be excluded with
  public.css in custom designs to avoid coloring of all normally visible links.
  [thet]