Avoid redrawing (thus loosing the selection and scroll position) of
preview window on style change by defining the colors through CSS styles.
On style change we just update the CSS color definitions and preview will
update itself without redraw.
We used to do this before WebKit and it looked better.
Also fix up the header section for right-to-left locales:
put the collapse button on the right, and images on the left.
All mail-parsing and formatting code has been moved to em-format.
Parsing is handeled by EMailParser class, formatting by EMailFormatter.
Both classes have registry which hold extensions - simple classes
that do actual parsing and formatting. Each supported mime-type
has it's own parser and formatter extension class.
