This reverts commit b37052d0.

This changeset introduces the concept of a "global" nuget package. The references to the NuGet packages are inserted into the Open VSL.Settings.targets file, which is imported into every project in Roslyn. This ensures that every project automatically gets these "global" packages. (changeset 1386548)

Updates System.Collections.Immutable and System.Metadata.Reader to versions 1.1.33-beta and 1.0.18-beta, respectively.
     Updates VSMEF to the latest build from VSPRO_1.

     A few code fixes:
     - ImmutableArrayInterop is gone
       - in product we used in a couple of places where we now just create a copy of the byte[] (MetadataWriter)
       - test infrastructure uses a workaround with explicitly laid out union to avoid copies of large metadata blobs
     - EditorTestApp class was incorrectly importing MEF components resulting in a cycle. The new VSMEF reports such errors. (changeset 1385613)

We had a number of projects that included the StyleCop NuGet package only to also disable StyleCop. We also had some projects that were referencing assemblies out of packages but didn't say so in packages.config, or had stuff in packages.config not reflected in the actual project file. (changeset 1378738)

***NO_CI***
 (changeset 1367677)

***NO_CI***
 (changeset 1356181)

This also updates Microsoft.Net.ToolsetCompiler to the corresponding version. (changeset 1355122)

When our projects were last updated to a newer version of Microsoft.Net.ToolsetCompilers, NuGet didn't replace the old version--it just put the new version next to it. Every project ended up referencing both versions, and which set of compiler binaries "won" depended on the order they appeared in the project file. So different projects built with different compilers.

This change strips out all references to the old version. (changeset 1352054)

***NO_CI***
 (changeset 1341082)

Change projects to reference the Proprietary Resources NuGet package versus the project. (changeset 1331358)

Update the version of the toolset compilers used for build and make sure that all projects are using the toolset NuGet. (changeset 1330804)

Update Test Resources Nuget package to Microsoft.CodeAnalysis.Test.Resources.Proprietary.0.6.4033103-beta
 (changeset 1219704)

Update the Roslyn Toolset to a version with an official, signed, NuGet package.

The new package is Microsoft.Net.ToolsetCompilers.0.7.4032713-beta.nupkg. (changeset 1217415)

Update Test Resources Nuget package to Microsoft.CodeAnalysis.Test.Resources.Proprietary.0.7.4032713-beta

Not strictly necessary, but it would be nice to be on the same build as the toolset compiler. (changeset 1217394)

The new package is Microsoft.Net.ToolsetCompilers.0.7.4032713-beta.nupkg. (changeset 1217346)

Update Test Resources Nuget package to Microsoft.CodeAnalysis.Test.Resources.Proprietary.0.7.4032705-beta (changeset 1216765)

Update System.Collections.Immutable 1.1.18 -> 1.1.20
Update System.Reflection.Metadata 1.0.8 -> 1.0.9 (changeset 1211547)

Removing duplicate entries from repositories.config (changeset 1211406)

Update System.Reflection.Metadata 1.0.8 -> 1.0.9 (changeset 1211431)