Add test utilities project

Copy from pytools project with minor modification for compiling.
Replace a C# test project by an F# one
Refactor to make the code easier to test
Add the first test for syntax coloring
Fix the issue with mismatched assemblies
Fix build errors
Clean up after rebase
Implement DTE mocks
Execute the first unit test successfully

Testing async code isn't very nice. One has to manually communicate
between async functions and NUnit test thread e.g.
http://jonas.follesoe.no/2007/09/18/unit-testing-event-based-asynchronous-code/
Refactor common logic to a test base class
Migrate VS tests to use NUnit

It should fix the issue with FSharp.Core version (MsTest doesn't
recognize binding redirects properly).
Add a few more tests
Fix failing tests by specifying existing files
Run multiple tests using the same test base
Remove extra param in VSLanguageService to avoid package failure
Address code review
Merge pull request #593 from dungpa/vs-tests

Initial version of Visual Studio unit tests