Improve extendability of NavigationMapRoute

[boldtrn]

The methods initialize and addListeners are called in the constructor of NavigationMapRoute. It should be possible to extend them and change how they work.

In the long run, we should probably consider moving most of the private properties to protected, as this class is responsible for the styling of the navigation experience and clients probably want to change how their apps look without too much trouble.

[frankkienl]

I agree protected can be better than private in certain cases. That way people can change these methods when extending the class 👍

Changing methods from private to protected, could also mean having to change some documentation. So let's keep that in mind as well 😉 !

[boldtrn]

Changing methods from private to protected, could also mean having to change some documentation. So let's keep that in mind as well 😉 !

Do you want me to change something here? We could mention it in the changelog, it is a small change, but could be worth mentioning?

[boldtrn]

@Brammos thanks for the review, I reverted the icon pitch change.

[boldtrn]

@Brammos, are you fine with this PR or should I change something?