Location service active after map disposal

[cpetrov]

When showMyLocation is set to true and the map widget gets disposed, location service indicators continue to show in the system UI until the application is closed.

[cpetrov]

This problem affects both iOS and Android.

[mpost]

The problem has been fixed on Android.

Awaiting tabris-ios change to properly receive dipose method in maps widget so that it can shutdown the location service.