Add 'Output' pane

[lilith]

Add 'Output' pane

Will include tabs for Jpeg, Png, and Gif encoding.

Jpeg tab will have 'quality' slider and 'progressive' checkbox.
Png tab will have 'colors' slider, 'interlaced' checkbox.
Gif tab will have 'colors' slider, 'dithered' checkbox

Matte color selector.

Width box
Height box
FitMode Combo
Scaling Combo

Save As button.

This will require refactoring how Panes handle 'suspendedKeys' and 'editingKeys'.