Viewer enhancements - key press functionality independent of input focus

[ubacher]

Viewer enhancements:

Define a set of key to work any where in the viewer no matter
which panel has the input focus:

Exit to return from viewer
Next/Previous image
All the T+x commands ?
Set input focus to image

And then one could provide the same functionality for using the mouse:
A set of buttons to do what the above keys do.