use custom action bar in single-pane to override default action buttons

Hide app icon when creating/editing. Also show a custom title on
tablets (multi-pane mode).

In single-pane mode, don't use a normal action bar menu. Set up
a custom action bar view with action-button-like buttons that
take up the entire horizontal area instead of clustering at the
right.

Bug: 5204581
Change-Id: Ia3de60cd28839d570697a7fd7f0ebc5d41c38b18