QImageElement:
 * if caller has specified onSelected block, use it instead of loading image picker when element is selected
 * fix imageViewButton configuration to fit image in button without changing aspect ratio
 * remove unimplemented image "touch up inside" code - should probably be optional if re-implemented
onValueChanged block should not be called until the actual value has changed.  This seems to match pattern for other QD elements.
Allow for QPickerElement items (spinner wheels) to be changed dynamically.

E.g. the first wheel could be "States" and the second wheel "Cities", where only the cities in that state are shown.  Each time the "States" wheel is spun to a new value, the "Cities" item needs to be updated.