Allow user to change theme in options #73
Description
The current hard-coded theme is "dark", there should at least be a "light" choice also, and possibly more choices in the future.
User picking a theme should cause different XML styles to be loaded, there is a "selector" tag for this purpose that I need to learn how to use.
Need to move all hard-coded color assignments from Java into XML to allow easy theme switching.
Maybe give support for user-made themes in the future.