Move AddImportStatement/RemoveImportStatement code to Common\MsBuildProjectUtility.cs so that
they can be used by both the VSIX and nuget.exe.
Bug-3848: Add .vcxproj and .jsproj to supportedextensions list which is used by NuGet.exe UpdateCommand
Update localized strings
In the get method of propety CommonResources.ResourceManager (Common\CommonResources.cs),
we need to change Single() to First() because, in the merged nuget.exe, there
will be multiple resources with the same name, which causes an exception without the fix.
Revert "Fix of issue 3174: Source Code Transformations must supports BOM."

This reverts commit 93202af9ca688ef4e8797f9ffa15801f4d2a6e55.
Fix of a MEF issue.
TabExpansion for DependencyVersion and FileConflictAction
script clean up
Help for DependencyVersion and WhatIf parameters
Fix of issue 3948: -Whatif does not work with downgrading packages.
Add more tests for install-package -dependencyversion.
Fix of issue 3954: "WhatIf" is installing packages in update-package multi-project scenarios.

The problem is that update-package will call UpdatePackage() on each
project in the solution, not just on the current project. Thus, the WhatIf
value should be set for each project before calling UpdatePackage() on it.

install-package only applies to the current project, so there's no problem there.
DependencyVersion can now be specified in nuget.config.
Further fix of issue 3954.

The reason why "Install Antlr 3.5.0.2" is displayed twice is that the
first one is output by package manager to indicate installing the package
into the packages folder, while the second is output by
project manager to indicate installing the package into a project.

The fix is to change the output strings to make this clear.
Fix the concurrenty problem that if there are multiple nuget.exe install running,
then the check for downgrade code would sometimes generate file in use
exception.
Make the value of DependencyVersion in nuget.config case insensitive.
Fix of issue 3978: Skip automatic package restore when build action is Clean.
Updated Acknowledgements.md with names/profiles for 2.8
Implemented VsPackageRestorer
Add support for Windows Phone 8.1 project. The framework folder for it will be WindowsPhoneApp81 or wpa81