Configurable Settings (Theme, Colors, Sound, and Display)

[vgmoose]

After #107, some settings to control the theme preferences and other configurable things is desired:

• Theme color (Auto (Based on system config), Light, Dark)
• Accents color (Auto (Red on Switch, Blue on Wii U), Red, Blue, other colors)
• Volume slider and Mute state
• Display resolution and text scaling
• Current language override

This is separate but related to #14, only due to the repo selector likely requiring a separate screen/modal to manage the list of repos. But I think the two pages would interact with each other.