More informative error messages

[steelahhh]

Getting an exception like this, makes it practically impossible to figure out the root cause

Rendering and children management is out of sync: requested com.bumble.appyx.core.navigation.NavKey@3a63756 but have only [com.bumble.appyx.core.navigation.NavKey@465492c, com.bumble.appyx.core.navigation.NavKey@10560079]

Would be nice to get more information in this message, e.g.:

1. more descriptive NavKey, mimicking toString of a data class
2. type and key of navModels that caused this exception

[KovalevAndrey]

Hey @steelahhh thanks for the suggestion, It indeed can be improved. PRs are welcome :)