Add zooming

[apsexton]

Add a zoom feature with actions

• zoomIn: increase the scale by one step
• zoomOut: decrease the scale by one step
• zoomReset: reset the scale to 100%
• zoomWidth: set the scale so that the full width of the image just fits in the window
• zoomPage: set the scale so that the full image fits in the window.
  All these actions just need to manipulate a scale variable and call a setScale method so that when drawing the image, it is drawn to the appropriate scale. Note that everything else has to be scaled accordingly: bounding boxes, scroll window preferred size etc.
  Both GTE and Layout sub-projects need essentially the same code.

[LibriCerule]

Will four buttons be used for each of these actions or will there be another way to implement this?

[apsexton]

You will need 5 actions. I would recommend 5 buttons, 5 menu items (perhaps in a new "view" menu) and appropriate keyboard accelerators.