loadTheme abstract method
Asynchronously load the theme data.
This method returns a Future that when complete will produce a
tuple of ZetaThemeData, ThemeMode, and ZetaContrast.
ZetaThemeData describes the colors that are used by a theme.
ThemeMode determines the brightness of the system.
ZetaContrast defines different contrast styles to use across the application.
Returns a Future ZetaThemeServiceData.
Implementation
Future<ZetaThemeServiceData> loadTheme();