Adjusting build warnings (#1780)
Adjusting build warnings (#1780)

* Changes error to warning because it's not necessarily fatal
* Does not warn if assembly has no code but contains embedded resources
* Adds a message code to supress with nowarn:OC2001 if needed
* Adds a message code to the other PackageReference warnings in the file
xkproject/Orchard2,stevetayloruk/Orchard2,xkproject/Orchard2,OrchardCMS/Brochard,OrchardCMS/Brochard,xkproject/Orchard2,xkproject/Orchard2,OrchardCMS/Brochard,petedavis/Orchard2,petedavis/Orchard2,petedavis/Orchard2,stevetayloruk/Orchard2,petedavis/Orchard2,stevetayloruk/Orchard2,stevetayloruk/Orchard2,xkproject/Orchard2,stevetayloruk/Orchard2