Add a third of the load command

Add a third of the load command

The load command encompasses the language spec, its parsing and building
the circuit representation (and it also should create the graphics for
the loaded part).
In this commit only a part of the parsing is done (and the
prerequisites such as input handling).
This now correctly(?) parses the input file into a catalog of parts with
their dependencies.
I am sorry for the big (and yet incomplete) commit.