Help: Create separate help widget class

That contains the tool bar together with a help viewer,
which can also be used for an external help window, and later be
extended to also replace the extra "central widget".

Change-Id: I73fac4c135b985cbe47062b90783f156b5062005
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>
Help: Implement a real external help window

With this patch it is just used with the context help "always show in
external window" option.

Change-Id: I4bc6ba8e0e241500f6970d4cb72f66ba02075ef5
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>