PackageManagement: Solution-level Packages

Support for Solution-level Packages
PackageManagement: Events, Exceptions, Refactoring
PackageManagement: OnPackageManaged
PackageManagement: Solution-level Packages Fix

IsPackageInstalled added support for solution-level package
PackageManagement: Fix name, remove obsolete code
PackageManagement: OK, need better refresh
PackageManagement: Refresh AvailablePackages
PackageManagement: cleanup
PackageManagement: cleanup again

Remove obsolete argument
PackageManagement: More cleanup
PackageManagement: Comply with test expectations
PackageManagement: notes
Backup
PackageManagement: Tests OK
PackageManagement: Fix refresh
PackageManagement: Remove too much events
PackageManagement: PackagesViewModel Events

Previous commit UpdatedPackagesViewModel events restored
PackageViewModel PackageChanged events removed
PackageManagement.Test: Ignore PropertyChanged
PackageManagement: more Refresh
PackageManagement: restore ViewModelBase to orig.