util/SArray: fixed wrong bound in copy ctor/operator,

removed useless `owns_data` member variable.  (I added `owns_data` before
I learned that instances of std::initializer_list are not guaranteed
to be static data structures.)

Also added some doc-comments and fixed some formatting.
live-test: dump sensors in received configurations, as well.
comms/ModuleControl: added an extra assert statement in `value_for`