Xamarin - Support references from PCL’s to NET Standard 1.0 to 1.6

Project.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>netstandard1.6</TargetFramework>
    <PackageTargetFallback>$(PackageTargetFallback);portable-win+net45+wp8+win81+wpa8</PackageTargetFallback>
    <DebugType>Full</DebugType>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Xamarin.Forms" Version="2.5.0.121934" />
  </ItemGroup>

  <ItemGroup>
    <Compile Condition=" '$(EnableDefaultCompileItems)' == 'true' " Update="App.xaml.cs">
      <DependentUpon>*.xaml</DependentUpon>
    </Compile>
    <Compile Condition=" '$(EnableDefaultCompileItems)' == 'true' " Update="MainPage.xaml.cs">
      <DependentUpon>*.xaml</DependentUpon>
    </Compile>
  </ItemGroup>

  <ItemGroup>
    <EmbeddedResource Update="CustomControls\CustomNavBar.xaml">
      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
    </EmbeddedResource>
  </ItemGroup>
</Project>