More DocumentsUI material iteration.

Move to using Toolbar for all actions.  Drawer contains its own
Toolbar with separate title, and hamburger is always visible.  Change
drawer items to match spec.  Switching to Toolbar allows us to remove
nasty dialog-on-tablet hacks, yay!  This also means we can finally
get real IME resizing support.

Move to using elevation for all shadows; this removes more nasty
hacks around drawing directory shadows.

Bug: 15836082
Change-Id: Iba70b898f385a7debd8aabfc98ff39d20bca860d