Overhaul Texture Loading Using Core's Image Functionality

[sonicfind]

Core now has the ability to load images files to memory directly. This helps immensely as we are no longer limited to Unity's basic features and provides a better interface to refactor with (and its faster).

One such refactor involves loading all applicable source icon sprites after a music library scan. We can do this because the sources to load are explicitly bound to the available songs. This makes the library much more seemless to scroll through.

• Fix fault album art async behavior - before this, any album art that would take a long time to load would halt scrolling through the menu. This no longer happens.