Support for styling MLNCompassButton

[danieleformichelli]

Is your feature request related to a problem? Please describe.
As far as I can find, the MLNCompassButton doesn't support any kind of style customization

Describe the solution you'd like
I would at least support a light vs dark mode similar to the scaleBarShouldShowDarkStyles which is available for the scale.
Another (but maybe more complex) option would be to allow specifying the tint color for the various piece of UI.

Describe alternatives you've considered
Implement a custom compass control, but it looks an overkill

Additional context
As we show other controls on top of the map and they are all white, I'd like to make the compass white as well

[louwers]

Thanks for the suggestion, a pull request implementing this would be welcome!