Add FrameworkController and related files to desktop builds of NUnitLite

This will allow the engine to run tests written against the NUnitLite framework builds under .NET 2.0 through 4.5. It doesn't affect CF or Silverlight.

Tests have been added and new projects for mock-nunitlite-assembly were created so that the tests can run. The old mock-assembly project used by the framework tests is now called mock-nunit-assembly.

This can be mreged without waiting for the engine to be updated - the feature will simply be unavailable till then.