Make ReferencePoint's Point3D copy constructor explicit. This implied
the following changes:
* Stock::get_reference_point(ReferencePoint&) becomes
get_reference_point(Point3D&). Reference points were always
retrieved by their coordinates only in the Stock anyway.
* Stock::find_create_reference_point(Point3D&) was added, since it can
have a different outcome than its (ReferencePoint&) counterpart.
* The unit tests for Stock were improved.
The function arguments were reviewed to add missing 'const' keywords,
and some classes were modified more deeply to make some pointer class
variables constant.
New autocalibration technique to generate points in line (use case:
underground tunnels). The handling of the
positioning.generate-reference-points has changed to be able to use
several autocalibration methods simultaneously.
Like in the other modules, we get rid of the old use of "access point".
This has user-visible changes, especially in the configuration (the name
of a few options has been changed).