Hi,

I'm using the latest master of gnome-music (built it today) and I'm running it on Fedora 20. Unline the gnome-3-12 branch, the UI of master is quite non-responsive and the app excessively hogs a CPU core.

- On first launch, it's in the "Albums" view. It takes 100% CPU and loads all albums. This takes a few minutes, after which I can scroll in the view, but scrolling is very slow and when scrolling, the CPU usage goes up to 100% again.

- Then I went into the "Artists" view. CPU usage went up to 100% again, and stayed on 100% for 10 minutes (after that I lost patience and killed it). In this view, the app responded to clicks very slowly.

Note: I have an approx. 30 GB music collection on this computer (some would say it's average, maybe for some people would say this is a lot), and it generally feels like gnome-music was not really tested with such use case in mind.

I can offer to help testing further iterations of the code. (Unfortunately, I don't know Python so can't help with optimizing the code.)