Bugs 20th feb

Fixed key bug(s) from testing on 19th Feb:
To test:
 - Start editing a new figure, without saving...
 - File -> Open -> Choose figure
 - Should get dialog to choose "Save" or "Don't Save"
 - If "Save" is chosen, get the extra dialog to choose a name

Also small bugs:
 - Dragging a panel, the X and Y attributes on the Info panel should be integers (not floats)
 - Also fixed formatting of zoom level when multiple panels of different zooms are selected.
 - Improved the 'Image not found' message if invalid ImageId entered in "Add Images"
 - Handle invalid imageId entered in the "SetId" dialog.