Integrate AddReferenceInFSI to VFPT

Close #897.

This is a faithful port of AddReferenceInFSI to VFPT.

I list here a few possible improvements for discussion:

 1. [ ] The menu item only appears in `References` nodes in Solution Explorer. Should we display it when right click on Projects as well?

 2. [ ] The feature generates references for all configurations in current project. Is this really necessary? Should we change to generate references for active configuration only?

 3. [ ] A few known assemblies are generated using full paths (see below).  Perhaps we should use assembly names only?

    ```fsharp
#r @"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5\System.dll"
#r @"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5\System.Core.dll"
#r @"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5\System.Numerics.dll"
     ```
 4. [ ] Hide the menu when the feature is disable.

 5. [ ] **Any other ideas you have in order to improve this feature.**


/cc @vasily-kirichenko @OkayX6 @halcwb 

I was referring to the capitalization rules for acronyms in the .NET framework guidelines :)
http://msdn.microsoft.com/en-us/library/vstudio/ms229043(v=vs.100).aspx