FIX: Introduce ISymbolScope instead of IDeclarationsCache (R#7->8 Migration step).
FIX: Minor modifications due to R#8 API changes.
FIX: Use of IProject extension method instead of UnitTestManager.GetOutputAssemblyPath(..) (R#7->8 Migration step).
FIX: Minor modifications due to R#8 API changes (part 2).