Remove debug statements and nicely end worker thread
Move parsing of syntax highlighting styles

Move parsing of syntax highlighting styles to own new class StyleParser.
This new class also supports retrieving a color palette for the text
editor from the style.

issue #3
Improved theme support

* Organize themes and styles in subfolders
* Automatic change of syntax highlighting theme when
  corresponding css style changes
* replace clearness and clearness-dark with solarized-light
  and solarized-dark

issue #3