1. Fix subtoolbar subtitle not always updating.
2. Fix colour of lists in dialogs when using Black theme.
3. Darker snackbar/toast background for Black theme.
4. Set splitter width to zero when queue hidden.
5. Tweak borders.
6. Show track tech info, and background images, if enabled, for track list when click on album name in now-playing.
7. If queue only has 1 item with no duration, then center the "1 Track" text.
8. If "track" custom actions are defined, then always keep composer, etc, details in now-playing for use in actions.
9. Only show "Go to composer", etc., items in now-playing context menu if configured to show relevant artist role.
10. Use alternative blur for now-playing backgroud, so that works with WebKitGTK.
11. Pre-cache HighDPI covers, thanks to Michael Herger.
12. Fix display of subtoolbar sub-title on biographies and album reviews.