The tool tip never has focus, so it cannot become the IContext that is
checked for context help. So, integrate the help id into Utils::ToolTip
and check the tool tip first when checking for context help.
As a side effect the [F1] button and help id for the tool tip is now also
available for use outside of the text editors.

Task-number: QTCREATORBUG-5345
Change-Id: Id975703caf161d1183c247e8ad8bb693b90fd306
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>