This essentially just puts the data members and most of the original
interface on the proper, i.e. the 'target', side of the tool/target
divide. Since the SimpleTargetRunner base already has an
ApplicationLauncher member, this can be used directly.

State handling and coordination between tool and target runner parts
stays as before for now, with unchanged 'custom' transition logic.
The plan here is to remove the custom state handling later, including
the two remaining cases of direct targetRunner->toolRunner calling
(startExecution, and adapterSetupFailed) for which this patch here
temporarily uses signal/slot connections.

Change-Id: I664f2e333b48b582befd0531a17d4008acac7c4c
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>