Move selection manager extras to separate package.

Tighten up public interfaces of classes.
Move BandController and GestureSelector to different package in-part to eliminate access
    to <default access> methods on Selection. Goal is to force all mutation operations through
    SelectionManager so that change notfication can be rationalize
    (and by "rationalized" I mean understandable).
Eliminate documentsui dependency in GridModel.
Eliminate another Java 8 dependency (IntPredicate). Consolidate w/ SelectionPredicate.
Don't implement listener interfaces directly in top level classes. use inner classes.

Bug: 64847011
Test: Passing.
Change-Id: I5291ad27fc1b39648d72eb87bff3c844b0af5ab9