Go back to individual Packages for React.Sample.Mvc6

- Since Microsoft.AspNetCore.All doesn't appear to mark .NET Framework 4.6.1 dependencies, I went and changed it back to individual package referencing

Author: ShikiGami

src/React.Sample.Mvc6/React.Sample.Mvc6.csproj

@@ -23,7 +23,12 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore.All" Version="2.0.0" />
+    <PackageReference Include="Microsoft.AspNetCore" Version="2.0.0" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="2.0.0" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc.Razor.ViewCompilation" Version="2.0.0" PrivateAssets="All" />
+    <PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="2.0.0" />
+    <PackageReference Include="Microsoft.VisualStudio.Web.BrowserLink" Version="2.0.0" />
+    <PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="2.0.0" PrivateAssets="All" />
   </ItemGroup>
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'net461' ">