Fix corenlp results parser (NLTK API change)

It looks like we used to rely on NLTK 2's ability to pass
a tree string to the __init__ function, but that this is now
a fromstring class method.
Expose functions used by STAC dialogue_acts script
FIX: regression in Orange csv output

The tab format uses 'd' for discrete, but the CSV one uses 'D'
Long term, we should just switch to the tabbed format everywhere,
but this may involve tweaking some of our infrastructure
More robust graphviz output.

Unfortunately pydot does not seem to quote graph names,
so we have to munge them to avoid confusing graphviz.
stac-learning weave: tweak attelo output

Mostly inject EDU text, but also strip group id and convert
offsets to int (attelo lets them be float in case you want to
give it something like timestamps, etc)