Python interface to the wire-cell command.
Configuration:
* WC file is a wire-cell configuration file in JSON format.
* WC JSON is the contents of a WC file.
* A configlist is the Python data structure representing a WC JSON
string. It is a list of dictionaries with keys "type", "name" and
"data" which holds a type-specific data structure.
* A configdict is a dictionary keyed by tuple(type,name) with a value
that of the corresponding "data" value.
The C++ Wire Cell components which are configurable provide a default,
hard-coded configuration "data" structure.