Compatibility with Unreal Engine 4.12.5

[menecken]

To make the Project compatible with the latest version of the unreal engine (as of now it's 4.12.5) the file

Plugins\RadiantUI\Source\RadiantUI\Private\RadiantWebViewRenderComponent.cpp

needs a small addition in line 46:

UWorld* World = GetWorld();

After that, building is successfull.