(visuOgreQt): use qt to create the OpenGL contexts for ogre

What does this MR do?

• Add a new class to create OpenGL contexts for ogre.
• Move the offscreen rendering manager to visuOgreQt and instantiate it through a factory.
• Fix material management for the VR widgets.

How to test it?

• Run fwRenderOgreTest
• Run OgreViewer, try out volume + surface rendering, switch between tabs
• Test an app using offscreen rendering

Additional tests to run

• GNU/Linux
• macOS
• Windows

Associated Issues/Merge Requests

• Issues

  • Fixes #361 (closed)
  • Needed for #336 (closed)

• MR

  • Depends on conan/conan-ogre!5