Spina 3.0 introduced a Result<T> = Backbone._Result<T> alias in

objects.ts, but it failed to import Backbone. This led to an

assumption that Backbone was a global type that should not be

interfered with, and thus renamed the Backbone type in the resulting

d.ts file tto Backbone$1.
This broke typing in some ways. Result<T> no longer had a type (since

it didn't know what Backbone._Result<T> was in this context), and the

difference between Backbone and Backbone$1 led to issues resolving

types of some attributes in subclasses of our base classes.
This change adds the missing import, fixing up the types.

Unit tests pass.
Verified this fixed typing issues in Ink.