Osu: Add song ticker to main menu

[smileyhead]

Describe the new feature: (This is something that's in stable, but not yet in lazer.) A ticker that would show up briefly (or indefinitely, if the user prefers) as a new song starts playing in the main menu.

Proposal designs of the feature:

[peppy]

Requires input from @arflyte

[arflyte]

Hmm, that works for now. I'll make a design for it so it fits well with the rest of the indicators at the corner.

[peppy]

If we go with the design in the screenshot, make it a gentle fade with no movement.