Add projects, .config, and .nuspec to .editorconfig

[MattKotsenas]

This change aligns the .editorconfig with what I observe from dotnet repos:

1. Adds *.config and *.nuspec to the XML section
2. Moves *.props, *.targets, *.config, *.nuspec out of the XML proper section and into its own section so that devs that have strong feelings about .xml can modify that independently
3. Added *.csproj, *.vbproj, *.fsproj, *.proj into a new section (I didn't add vcxproj since this focused on .NET development, but happy to add)