Also reduce the minimum height for the world when manually entering
a size -- it used to be a nanometer. The minimum exists so that
the world size never becomes 0. Perhaps this should be changed.

Also makes it so that, if every size is marked 'all forms',
changing forms doesn't reset to the form's default size.
This makes sense for characters whose forms are all the same
size.

This reverts commit b839cd88a1.

Also lets models have a default view for each form. Fixes some incorrect
behaviors with the setup of entities to go along with this (e.g. if there
was no default form, the last form would wind up being the default, rather
than the first, if default views were specified.

Also sort some of the vehicle categories, and the vehicle
group itself.

The importer reads a directory of .zip files and imports each one to its own collection.

About to change the capitalization of a directory name, so I am separating this
into its own commit. Fun.

Instead of using the built-in camera fitting function,
which wants to rotate the camera, it now calculates the
local bounding box of the object for each camera angle.