Entities can now be rotated. This does not affect
their height. For now, they can only be rotated by
45 degrees at a time. I will work out something nicer
later on.

This affects the world height, the entity scale, and all view numeric inputs.
The fields are no longer of type 'number' so that text can be entered.

This stops Firefox from complaining that the values
are not integers.

Also tweak the function for making groups of entity so that
it only adds model scales for vehicles, and so that the directory
it works in can be set. This still needs to be spun out into a more
generic function, though.

Mostly spans with divs as children, as well as writing
checked='true' instead of just checked.

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