Added caching of trained classifiers. We do not want to be using this commit. The cluster can run all of our experiments at the same time, and the fix enables us to run the first two experiments at a slow rate and the rest much faster. Not worth it, esp given the possibility of a wrong cache retrieval due to the very complex cache key
fixed two bugs:
1) default for include_self in conf file was True, which meant SignifierOnly and SignifierSignified token handlers in the OOV-IT case collapse down to including the seen feature only (also changed some defaults in confrc to match what we are doing now)
2) with recent changes to thesaurus_loader.py, a thesaurus returns a list for any query, but the list may be empty to indicate there is no such entry. BoV vectorizer relied on thesaurus returning None to signal an OOT token. This means all tokens were considered in-thesaurus.

The two above combined result in identical behaviour of SignifierOnly (exp 26, 27) and SignifierSignified (24,25)