Provide the ability to specify a zoom level other than the ones provided in the pictureTool() window

[dllargent]

The pictureTool() function currently displays an image in a window, and among other things, has a "Zoom" command that allows the image size to be reduced to 25, 50, or 75 percent, or enlarged to 150, 200, or 500 percent of the original image size.

This enhancement will allow the user to select a zoom level that is not one of the provided values. The selection could be made by the user entering a number, or moving a slider. Some limited boundary checking should be performed. For example, the zoom level should not be zero or negative.