Hiring a temp... (Allow property values to be marked a temporary)

This is a small change to allow property values in Added entities to be marked as temporary. The code reuses generalized IsModified storage since that flag is only used in Modified entities while this flag is only used in Added entities. See https://github.com/aspnet/EntityFramework/wiki/Entity-Framework-Design-Meeting-Notes---July-10,-2014#value-generation
Improvements to entity tracking of query results.

- Entities not returned by the outer result set are no longer tracked.
- Introduced a query StateEntry buffer to isolate query execution from the StateManager.
Remove PathResolver
Target aspnet50
Update .csproj files
Migrations: Add K commands
Hack together a demo