Tooltip support.

Basic tooltip support for widgets relying on the existing QToolTip
mechanism.
Left unimplemented on the Qt Quick side for now since ToolTip support
is still very much a work in progress there.

Change-Id: Ia4bfd715a224e0cbc147c8860e131d1545cebe1e
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>
UI: fix a crash on shutdown

Use a raw pointer instead of QScopedPointer for the UI components.
Since the components are always parented to the view and deleted through
the QObject cleanup mechanism, it was not correct to use QScopedPointer
in the first place.

Change-Id: I0c8fd9526e898439c52c6a6f538a66f8a1185ef9
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>