Add nuget.org package source and mapping to NuGet.config

Author: pwelter34

NuGet.config

@@ -1,8 +1,12 @@
 <configuration>
   <packageSources>
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
     <add key="foundatio-feedz" value="https://f.feedz.io/foundatio/foundatio/nuget" />
   </packageSources>
   <packageSourceMapping>
+    <packageSource key="nuget.org">
+      <package pattern="*" />
+    </packageSource>
     <packageSource key="foundatio-feedz">
       <package pattern="Foundatio.*" />
     </packageSource>