PackageId for official netDxf nupkg

[devel0]

With this PR the PackageId field added to csproj with the name netDxf-official that isn't used on nuget as results from this search https://www.nuget.org/packages?q=netDxf

Publish nupkg is pretty simple:

• register your free account to https://www.nuget.org
• create a api key and save to a safe location outside the source tree ( mine is a 46 characters length api key ) ; you can reuse every time to publish new versions and you can revoke and generate new ones from user profile on nuget account.
• do following commands ( replace APIKEY with your api key ):

cd netDxf/netDxf
dotnet pack -c Release
dotnet nuget push bin/Release/*.nupkg -k APIKEY -s https://api.nuget.org/v3/index.json