Remove reference to startingPage from NavigationGraphGenerator error message.
ERRAI-718: Create type for transition to role and verify existence of UniquePageRoles at compile time.
Enforce existence of LoginPage and SecurityError pages at compile-time in errai-security-client.
Remove general, non-typesafe navigation methods from SecurityContext.

These methods have been replaced with methods for navigating
specifically to the LoginPage or SecurityError page. Also added another
method like "navigateBackOrHome" that allows you to navigate back or to
a provided page.
Add failing security test for SecurityContext page caching.
Fix failing security navigation test. SecurityContext goes to correct page after navigation is denied.