set paths to angle and d3dcompiler dlls via QLibraryInfo

angle requires 1 to 3 dlls: d3dcompiler_4X.dll and possibly libGLESv2.dll and libEGL.dll

the location of d3dcompiler can only be specified via an environment variable. GLESv2 and EGL are loaded from the default library paths only.

• we need to find a way to specify GLESv2 and EGL paths when running qt inside a plugin
• when running qt inside a plugin, we cannot be sure that we are the only ones who are using environment variables (e.g. the host might have set this variable). to come across this limitation, a c++ interface to configure the locations would be great. morten sørvig suggested the QLibraryInfo class as a possible location