Turn theming on or off

[astrohart]

Adding an IsThemed property to everything would be great, so we can turn the theming on or off. By which I mean, either to use the colors/design in this library (dark theme) or default, e.g., Windows system colors, or some other theme.

[softwareantics]

@astrohart hey, I'd like you to know that since it looks like this project has gone stole I've forked it here. This is likely going to be a feature I will add. If you like, just log an issue over on my fork :)