Theme support

[oxr463]

Let's add the ability to theme the app, possibly to match some of the Roku themes.

[JohnVeness]

A dark theme would certainly be nice.

[JohnVeness]

A dark theme would certainly be nice.

When I wrote this I was on Android 9, and apps didn't pick up the theme from Android Settings in that version. Now I'm on Android 13 it does now pick up Dark mode from Android Settings, so this is fixed for me, but I guess for anyone else still on older versions it would be nice to at least have a Theme choice of Dark, Light, and Follow system, as many apps do.

[pupitetris]

Also under dark mode, the accent color (purple) has very low contrast with dark gray, so there are some controls that are difficult to read on dark mode. The fix for this is in my to-do list.