Initial changes to rework the design time host
- Account for multiple target frameworks
Fixed framework name members
Refactoring message types
- Separated References and Dependencies messages
- Changed ProjectName to Name
- Changed ConfigurationData to a list of strings
Support the runtime retrieving compilations per target framework
- Added SendCompiledAssemblies and SendDiagnostics  for clarity
Added target to project references in design time host
- Round trip LibraryDescription description and added FrameworkName to
LibraryDescription.
- Set the target framework when resolving the project references and
always fallback to the requested framework
- Represent project references by a ProjectReference type
in DesignTimeHost instead of a string.