Add support for night and dusk modes

[bc38]

Wishing to reduce the brightness of the radar image when you change the color scheme. http://www.cruisersforum.com/forums/attachment.php?attachmentid=129438&d=1471022937

[keesverruijt]

Since we can't change the way that buttons work in the OS and they cannot be made darker, there is no point in doing this until we find a way to replace buttons with something else, as the menu won't be able to adapt to night mode.

So this is not a trivial change.

[bc38]

I mean radar image See a screenshot of the link as it might look like