Add mouse control for field of view
Add mouse control for field of view

Hook up Shift + right mouse button to convert vertical motion into changes
in field of view.

pbfy0/visvis,pbfy0/visvis.dev,pbfy0/visvis,Alwnikrotikz/visvis.dev,chrisidefix/visvis,chrisidefix/visvis,AlanZatarain/visvis.dev,almarklein/visvis.dev,chrisidefix/visvis,Alwnikrotikz/visvis,Alwnikrotikz/visvis,pbfy0/visvis,Alwnikrotikz/visvis,chiluf/visvis.dev