When mouse is over backside frontside highlighted
When mouse over frontside backside highlighted
Frontside highlighting conditionalised

Not highlighted if backside is on the backside of another widget.
Various failed drop feedback attempts

Trying #50 but not easy since frontside children get in the way.
Drop feedback added

Fixes #50.
Semi-transparent while being dragged

Looks nicer
Hide button removes highlighting
Added support for dragging image files

Most of #57. Still need to deal with text files.
Added support for dragging non-image files

Either text, HTML, or ToonTalk JSON
Fixed a just introduced drop location bug

When dragged from resources ended up higher than it should be.
No drop feedback for drop on self
Better workaround to dragleave problem

By temporarily turning off events for all descendants.
Replace JQuery 'on' with 'addEventListener'

Because Chrome Developer tools Elements inspector has links to where the
events are added.
Drop feedback broke empty holes

So boxes no longer display drop feedback.
Canonicalise  element attribute values

Currently only angles are constrained to between 0 and 360. Will be good
for conditionals. Fixes #56.
Backsides resize better

Everything is scaled. And restored when hidden and re-opened.
Drop in another windows fixed

Support for dropping files broke it.
Backside geometry is now added to JSON

And hence preserved and transferable.
Improved backside resizing
Text areas are now white