minor fixes

- headerbar bottom edge bevel
- document button extend
- move generic parts to the top
tab transitions, use fewer static colors
some more button experimenting
redone buttons once again, hope this tie will last a little bit longer :-)
added text emboss effect helper function and some error fixing in the button drawing function
bring back the soft focus for entries
set nicer text-shadow colors
simplify button drawing

- colored buttons should not require separate duplicate states.
make sure $borders_color is respected in button
drawing.

- i believe that's what Lapo has been trying to
  tell me all of today.
make sure to pass the colored attribute for seuggested/destructive
get rid of old playground stuff
let's not define same thing in two places
initial implementation of spinbuttons
sane labels ;)
tweak colors on all button states.
make dark button less raised
simplified button text shadow function, dimmed insensitive active button background
fixed box-shadow on insensitive buttons, fixed missing text/icon shadow on combos
dimmed backdrop fg color
Fixed entry selected text, implemented entry backdrop states.
Sassified comments so they won't appear in the generated css.