Fixing the unit tests

The call to DisposableTimer.DebugDuration() in
ArchetypeValueConverter.ConvertDataToSource() expects the propertyType
parameter to be not null, but the implementation of
ArchetypeValueConverter.ConvertDataToSource() allows the propertyType
parameter to be null. This breaks some of the unit tests.
I've added a null check in the call to DisposableTimer.DebugDuration()
to counter this issue.
Add default value overload to GetValue()

Fix issue #142
Fix code formatting
Fix 'hide property label'
Fix for #160