Implement Nuget Package UI

[danwalmsley]

Note: We already have nuget apis in use for our PackageManager class, so we should try to use the same version of this api.

• [ ] Context menu for project and solution extended via plugin. --- This might need to be a separate PR.
• [ ] Able to show referenced packages in the references in Solution Explorer
• [ ] Able to show packages installed on per project basis in package manager ui.
• [ ] Able to show when updates are available.
• [ ] Able to show packages installed and updates solution wide.
• [ ] Search for and install packages
• [ ] Uninstall packages
• [ ] nuget.config support
• [ ] manage nuget source

[danwalmsley]

If we need to mod the csproj as we do this... https://github.com/jchannon/EditCsProj/tree/master/src/EditCsProj

Might serve as a nice reference

[FlaviusHouk]

What do you think about using msbuild parts (Microsoft.Build and Microsoft.Build.Utilities NuGet packages) to work with references? This also relates to #646 .

With code like this

Microsoft.Build.Evaluation.ProjectCollection projColl
                = new Microsoft.Build.Evaluation.ProjectCollection();

var pathToProj = "/some/path/proj.csproj";

var p = projColl.LoadProject(pathToProj);

var packages = p.GetItems("PackageReference");
var projs = p.GetItems("ProjectReference");

All required information might be obtained.