Don't show recents as copy/move destination.

Revoke "SUPPORTS_CREATE" from the Recents faux-Root.
Don't allow copy to roots that don't support children.
Add friendly access methods to Root info for checking flags.
Only show spacer between roots sections when both non-empty.
Add docs explaining the "apps" section in roots.
Improve logic in the "canCopy" method.

Bug: 27232639
Change-Id: If78ee0ff73f0788de863345b560aecd41b23dfb9