Use nlohmann.json NuGet package instead of direct file

This way it will be easier to update to new version (when released).
And it will be also clear that we have dependency on this 3rd party
library.

Author: ge0rdi

Src/Lib/DownloadHelper.cpp

@@ -13,7 +13,7 @@
 #include "FNVHash.h"
 #include "StringUtils.h"
 #include "Translations.h"
-#include "json.hpp"
+#include <nlohmann/json.hpp>
 #include <wininet.h>
 #include <softpub.h>
 

Src/Lib/Lib.vcxproj

@@ -101,7 +101,17 @@
     <ClCompile Include="TrackResources.cpp" />
     <ClCompile Include="Translations.cpp" />
   </ItemGroup>
+  <ItemGroup>
+    <None Include="packages.config" />
+  </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
+    <Import Project="..\packages\nlohmann.json.3.11.2\build\native\nlohmann.json.targets" Condition="Exists('..\packages\nlohmann.json.3.11.2\build\native\nlohmann.json.targets')" />
   </ImportGroup>
+  <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
+    <PropertyGroup>
+      <ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
+    </PropertyGroup>
+    <Error Condition="!Exists('..\packages\nlohmann.json.3.11.2\build\native\nlohmann.json.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\nlohmann.json.3.11.2\build\native\nlohmann.json.targets'))" />
+  </Target>
 </Project>

Src/Lib/Lib.vcxproj.filters

@@ -149,4 +149,7 @@
       <Filter>Lib</Filter>
     </ClCompile>
   </ItemGroup>
-</Project>
+  <ItemGroup>
+    <None Include="packages.config" />
+  </ItemGroup>
+</Project>