[CSharp] Don't add explicit references to new PCL project

All the framework assemblies are referenced implicitly.
[Ide] Hide PCL framework assemblies from Edit References dialog

They're all referenced implicitly, user should not be allowed
to add duplicate explicit references.
[Ide] Ensure ".NET Portable Subset" node is shown for PCL projects
[Ide] Allow expanding ".NET Portable Subset" tree node

Shows an error when framework not installed
Allows opening assemblies with assembly browser
[DeignerSupport] Add property panel support for PCL assemblies
[Core] Ensure process output redirected when reading output

Should fix BXC14561 - Xamarin Studio crashes with (Remote) Soft Debugger custom command