Improve script editor theme selector

- Use a drop-down list instead of buttons
- Add option for only changing the font colour and background

Issue #29
Style also folding markers
Add option for styling also selected text's foreground

That is, override selected text's own colour styling.  Disabled by
default in order to avoid drama.
Use the same style for selected text on the scrap window than on the script editor

Previously it was hard-coded. Ideally it would be a new independent
style (and same for flashing new text), but let's try to not add more.
I'd recomend setting the 'scrapbook window' colour style the same as
'current line highlight'.
Use different font face defaults on Windows and *nix

Also some minor changes to the default theme:
- Comments use a serif font (on Windows this means Georgia instead
  of Comic Sans MS)
- Numbers, line numbers and scrapbook use a monospace font
- All function names are bold
Add two new script editor themes

The new themes are based on
Solarized <http://ethanschoonover.com/solarized>

Issue #29
Fix rare exception on parsing of functions with bad syntax
Add a new script editor theme

Based on Zenburn <http://slinky.imukuppi.org/zenburnpage/>

Also, use a sans-serif font for __END__ comments on all themes

Issue #29
Fix using wx.stc.StyledTextCtrl.SetSelForeground on wxGTK