macosx: Colour all accented UI items consistently

In the library window we still have some elements with hard-coded colour values and use some images that are coloured for repeat/shuffle states.

This MR addresses these and ensures they are consistently coloured with the application's accent colour, which also adapts to the system accent colour.

Examples with green system accent colour below

Before fix:

After fix:

Signed-off-by: Claudio Cambra developer@claudiocambra.com