Set "disabled" background to "lightgray" for consistency with the dialog
background. The inconsistent background can be seen in the file search dialog
with an empty search string.
The hotkeys in dialogs were impossible to distinguish from other text. Make
them red for consistency with the buttonbar.
Show changed lines in diffs in black on cyan. Blue on cyan is hard to see,
such color combination is not used elsewhere in the skin, which promises
"good contrast".
Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
