IsValid state should be determined by both session and content
Cleaned up action queue manager disposal.
Cleaned up content initialization.
Created second testing page to play with.
Testing navigation
Making sure knowntypes doesn't have any doubles.
Moving invalid check to the session's viewmodel so it can be reused.
Split up ViewModel into partial classes because it was getting a bit big.
Should be an argumentexception instead.
Page initialization.
Using textblock as the header
TabControl requires layoutrounding to look its best.