UICommon: Add AutoUpdate module + placeholder Qt implementation

The AutoUpdate module is a generic update checker mechanism which can be
used by UI backends to trigger an auto-update check as well as the
actual update process.

Currently only configurable through .ini and the Qt implementation is
completely placeholder-y -- blocking the main thread on a network
request on startup, etc.

Source/Core/UICommon/UICommon.vcxproj

@@ -42,8 +42,12 @@
     <ProjectReference Include="$(CoreDir)Core\Core.vcxproj">
       <Project>{E54CF649-140E-4255-81A5-30A673C1FB36}</Project>
     </ProjectReference>
+    <ProjectReference Include="..\..\..\Externals\picojson\picojson.vcxproj">
+      <Project>{2c0d058e-de35-4471-ad99-e68a2caf9e18}</Project>
+    </ProjectReference>
   </ItemGroup>
   <ItemGroup>
+    <ClCompile Include="AutoUpdate.cpp" />
     <ClCompile Include="CommandLineParse.cpp" />
     <ClCompile Include="UICommon.cpp" />
     <ClCompile Include="Disassembler.cpp" />
@@ -55,6 +59,7 @@
     <ClCompile Include="GameFileCache.cpp" />
   </ItemGroup>
   <ItemGroup>
+    <ClInclude Include="AutoUpdate.h" />
     <ClInclude Include="CommandLineParse.h" />
     <ClInclude Include="UICommon.h" />
     <ClInclude Include="Disassembler.h" />
@@ -70,4 +75,4 @@
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
   </ImportGroup>
-</Project>
+</Project>