replace "model branch" with "model subtree"

[OwenInCanada]

Hi all,

I suggest replacing "model branch" terminology with "model subtree" in documentation and menus. This avoids confusion with the widely used version control term "branch" that has a completely different meaning.

(The most confusing function in this regard is "Package control / check in branch".)

At the very least, it would be helpful if the documentation gave an explicit definition of branch: "A model branch is a subtree of the model in the project browser hierarchy."

Regards,

Owen