Resolve "Remove deprecated documentation in VRRender apps"

What does this MR do?

Clean the old documentation of VRRender:

• remove Apps/VRRender/doc folder
• remove Acknowledgments and VR-Render Website actions
• update about documentation to remove the link to fw4spl

Closes #181 (closed)

How to test it?

Launch VRRender and click on the menu Help/about.

Some results