Allow skins to set different status bar backgrounds for player screen and library

[LPW00]

Apparently, this can currently be done for android's navigation bar, but not the status bar.

Use case:

A user (me) might want to have a fully transparent status bar background on the player screen, but a tinted or solid status bar in the library because otherwise the the status bar is unreadable when you scroll over a particularly bright (or dark if you use the light theme) background or the album names etc which might have the same text colour as the status bar.