[Feature Request] Theme support

[retropassdev]

If possible implement theming and support for dark/light modes.

Themes

• control visual styles of various components, like list views, item containers, etc...
• specify colors, font styles, size, etc...

Modes

• each theme should have Light and Dark mode, so it conforms to system selected mode
• option to override default mode. For example, even if xbox mode is Light, use Dark skin for retropass

Currently, all color values and control styles are hardcoded into xaml files. Move out all the visual elements into theme packages which can be replaced. Themes could be selected from the settings menu.

Ideally, themes and modes would be replaced in runtime but if it is difficult to implement, app restart might be required.

Ideally, themes and modes would be loaded dynamically as loose XAML files. This would avoid whole app recompile and promote easy theme sharing as it would only be required to point retropass to a set of resources.