Rewrote b-tree today, new nominclature

Rewrote b-tree as an app object, but about half the time was spent or factoring common code out of what used to be called list. So both classes are now much lighter than before.

I'm also renaming things. CowDb will support 3 kinds of persistent maps:

1. ORDERED --this was the old list. It allows you to arrange its keys.
2. SORTED--used to be large table. This is an implementation of the b-tree algo.
3. HASH--used to be large hash. Still to be implemented, likely this weekend.

Now I've also extended the metadata in factory a tad so you can specify the internal node type to be used by SORTED and HASH. This eliminated the need for wellknown, links and backlinks classes.

Cheers!