Migrate FxCop to FxCop analyzers

[tsahi]

The project originally used FxCop to enforce code style. This has been deprecated, and replaced with FxCop analyzers. We should find what rules were used with FxCop, and apply the same rules with FxCop analyzers.

We should prefer the NuGet package of FxCop analyzers, so developers don't have to install extensions for this to work, and so it works when running msbuild from the command line.