Fix #101 , which was introduced when fixing #95.

There is a limitation in the OS on how resizable sheets render and current solution is to handle regular sheets separately from resizable sheets. Regular sheets will persist when backgrounding the application (as expected behavior) but Resizable Sheets will be recreated. This appears to be a bug in the OS and fixing it would end up breaking the resizable sheet UI.

As a conclusion, developers should generally not segue to children within resizable sheets, as they will be recreated when app is backgrounded. Possible use resizable sheets as mid-screen modals that dismiss before segueing elsewhere.

Full Changelog: https://github.com/SwiftfulThinking/SwiftfulRouting/compare/6.1.6...6.1.7