Add ui::Color and ThemeColor, move Color to app::Color

Now colors are customizable from skin.xml file.
Remove bevel_box() and SkinTheme::draw_bevel_box()
Remove character_length() and render_character() functions
Move draw_progress_bar() to SkinTheme::drawProgressBar()
Remove SkinTheme::less_bevel()
Replace UndoConfigProvider with UndoHistoryDelegate interface