- This dialog is needed to extend the annotation support to adding image annotation.
- Expects user to enter url; calculates width and height of image
- Includes image dialog input validation; checks url, width, height

... in the image annotation input/edit

- If the constrain proportions checkbox is checked in image annotation input, this functionality will make sure that the image proportions are maintained if either a new width or height is entered
- These image annotation insert/edit changes attempt to implement image insert/edit workflow similar to Mirador 2