Workers handle errors better, code is cleaner

Concordance can now track when its worker fails. Scorer cannot, but doing it right
(both of them) may involve a sort of ticketing system for each job associated with
a concordance or a run.

This commit also fixes many issues and improves (& corrects) the validation module
and associated code.

Related to #15, but to handle #15 well requires tracking jobs better. Not sure it's 
worth the energy expenditure right now to do that. 
Hmm, not sure about this. It's not something I've really seen done, and in this case I'd just be moving information and the potential spelling mistake from one part of the file to another. Anyone else have input?