Add TakeFocus in WebContentsViewQt for passing on tab focus.

Chromium calls RenderViewHostDelegate::TakeFocus when the
last focusable item within the page was reached.
We then have to move the focus on to the next/previous
QQuickItem.

Change-Id: Id0128053602ff1220c1bced1b218050b66fef659
Reviewed-by: Andras Becsi <andras.becsi@digia.com>