This simplifies the way that we publish files to our network drop share.
Changes:
* Instead of explicitly listing every file that needs to publish, use directories to classify packages and artifacts into different categories.
* Add documentation for the expected layout of artifacts/
* Remove the need for static analysis to determine which packages go to which project
* Add the MSBuild property "IsProductPackage" to .csproj files which ship as a package to NuGet.org.
Changes:
* Sign shared fx zips
* Sign metapackages
* Disable signing on inner repo builds and instead sign all packages at the end
* Add a list of files from other Microsoft teams which can be excluded from signing
* Add a list of 3rd party assemblies which are bundled in the shared frameworks.