They'll always be 3/10ths as tall as the world is.

This also gets rid of the groups, which were messing up the layout.

All of the entities are rendered to the canvas. It only renders images, so there are no
names, height bars, etc.

You can paste an image into the window to get a temporary entity.

They now move the camera left and right, rather than shoving everything
left or right

One entity was having its info shown, even though it was not selected

Entities now have their templates cloned (by serializing and parsing) to allow for
a single object to be passed in repeatedly.

displayEntity() now only triggers a refresh of the world if asked, and
the scale is only redrawn if the world's size has changed

Also makes the scale input behave like the rest - change, not input

Otherwise, you could load a giant scene, close the browser, and be stuck with
it forever!

This reverts commit 4c58eb9b94.