Reimplement OAuth2 library - Step 1

Src/GoogleApis.Authentication.OAuth2/GoogleApis.Authentication.OAuth2.csproj

Index: Src/GoogleApis.Authentication.OAuth2/GoogleApis.Authentication.OAuth2.csproj
===================================================================
--- a/Src/GoogleApis.Authentication.OAuth2/GoogleApis.Authentication.OAuth2.csproj
 b/Src/GoogleApis.Authentication.OAuth2/GoogleApis.Authentication.OAuth2.csproj
@@ -99,7 99,11 @@
 </ItemGroup>
 <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
 <Import Project="$(SolutionDir)\.nuget\nuget.targets" />
- <Import Project="..\..\packages\Microsoft.Bcl.Build.1.0.8\tools\Microsoft.Bcl.Build.targets" />
 <Import Project="..\..\packages\Microsoft.Bcl.Build.1.0.10\tools\Microsoft.Bcl.Build.targets" Condition="Exists('..\..\packages\Microsoft.Bcl.Build.1.0.10\tools\Microsoft.Bcl.Build.targets')" />
 <Target Name="EnsureBclBuildImported" BeforeTargets="BeforeBuild" Condition="'$(BclBuildImported)' == ''">
 <Error Condition="!Exists('..\..\packages\Microsoft.Bcl.Build.1.0.10\tools\Microsoft.Bcl.Build.targets')" Text="This project references NuGet package(s) that are missing on this computer. Enable NuGet Package Restore to download them. For more information, see http://go.microsoft.com/fwlink/?LinkID=317567." HelpKeyword="BCLBUILD2001" />
 <Error Condition="Exists('..\..\packages\Microsoft.Bcl.Build.1.0.10\tools\Microsoft.Bcl.Build.targets')" Text="The build restored NuGet packages. Build the project again to include these packages in the build. For more information, see http://go.microsoft.com/fwlink/?LinkID=317568." HelpKeyword="BCLBUILD2002" />
 </Target>
 <!-- To modify your build process, add your task inside one of the targets below and uncomment it.
 Other similar extension points exist, see Microsoft.Common.targets.
 <Target Name="BeforeBuild">