This makes the upcoming Java bindings simpler and improves parity with
existing API conventions.
Note that camutils does not depend on filament and therefore cannot use
BuilderBase.
Note that the Manipulator Builder state is public which breaks with
convention but makes implementation simple and allows C++ clients to
continue using modern initializer syntax if they wish.
This moves the camera manipulator into its own library and adds new
functionality including a new "Google Maps" manipulator and a bookmark
feature to facilitate camera animation.
Java bindings and an Android sample will land later this week.
