To use this just drop a local image file onto the spot on the add dialog that says "drop here".
The panel can't display /ipfs/ URLs, so they appear as broken images. Need to use models to display them.
* Replaced window.open with a blank window and the populated that with an ImageAdder react component.
* Switched the image list to be part of ImageMenu's state so it can be dynamic.
* Added a little form to that component that lets the user enter a URL. When they hit "submit", add that to the image menu.
