GoRouter -- there should be a way to "push" a subtree

[Wishmater]

this means the subtree will decide its normally with .go, but wont affect routes below it in the stack.

PROPOSAL:

• create a new custom routeDelegate, that contains a goRouterDelegate and conveys everything to it
• add a new method pushRouter: allows to push a new goRouter, with full functionality, on top of the existing one. When the last page of this new router is popped, the whole router will be popped, returning to previous one
  • add an aditional initialRoute parameter when pushing new router