Instead of passing around kwargs to root WBE classes and to
contained classes prefer to use explicitnamed arguments that are
passed around. This makes the code more obvious as to what
the intended arguments are and makes it easier for error validation
when other unknown arguments are passed (as well as for docs).
Also moves the docs for the worker engine to be a sub-TOC under
the main engine document so that it can be more easily explored
and managed/found...
Change-Id: I9413fad187c330fee494f0d4536cc27d9a90f0fb
addc286409