Extends standard webview to detect scroll direction.

1. Some bugfixs, i.e null check for getChildAt(0) in ensureTarget().
2. Added loading indicator for app-list. Added layout for header of
app-list.
3. Added new logical for showing and hiding actionbar. When scroll-up,
hiding, then showing scroll-down until Y of view onto 0.
4. Removed old logical that used Touch for showing/hiding actionbar.