Add toggle for user interface display

- "/" toggles UI (incl. stats if displayed); menu View > User Interface
- "%" = toggle status; menu View > Stats
- Acts on normal, 3DTV, and Oculus display.
Fixed performance timer scope
Resize the overlay framebuffer when the application window is resized
Guard _framebufferObject deletion
Integrate UI toggling menu item and Hydra UI toggling

They work together and both fade the UI in / out.
Merge pull request #3138 from ctrlaltdavid/19836

Code Review for Job #19836