Enable changing route providers after initializing a FerrostarCore instance

[ianthetechie]

Discussing with a developer using Ferrostar, they expressed frustration that they had to create a new instance of FerrostarCore for every mode of travel their app supported.

A possible solution for this is to have an overload to startNavigation which lets you set a new profile / route adapter. We cannot make this a settable property at any other point in the flow safely though, because this would create very bad surprises during recalculation.