Add AggregateMotionState for treating many MotionState streams as a single…

Authored by featherless on Mar 15 2017, 1:50 PM.

Description

Add AggregateMotionState for treating many MotionState streams as a single stream.

Summary:
Draggable and Spring now both make use of the type in order to implement the Stateful protocol.

Make all gestural interactions Stateful.

Reviewers: O2 Material Motion, O4 Material Apple platform reviewers, Material Motion, chuga

Reviewed By: O4 Material Apple platform reviewers, chuga

Subscribers: chuga

Tags: Material Motion

Differential Revision: http://codereview.cc/D2879