app: Adds MPRIS support for remote control

cmake: Adds a install/compile step for the gsettings schema, and adds a nix flake

Adds a nix derivation

Save window settings to preferences

Save stations sorting preferences

Model: include missing header in model.hpp

Fix playback resume back after inactivity

Fix occaisional crash when updating

CMakeLists: Should check for `xxd` existence properly

Otherwise it will fail to build in strange ways (won't run xxd and build fails
looking for resources/blah.h).

Bye bye futures

UI tweaks

Show currently playing track in UI

Don't allow sorting of the artwork column

Fix crash when closing the window

Fix tooltip

Fix build on Arch systems

Use lowercase name for window title

Channel artwork support

Beginning work on artwork

Update README