This commit adds a 'parent_view()' function to the loader session, which
allows to set the parent view of the subsystem's Nitpicker view.
If the function is to be used, this must get done before calling
'start()'.
Fixes#1172.
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082
