Configurable pref

requires https://github.com/OpenTreeOfLife/peyotl/pull/33
allows config dependent specification of a new study prefix, but that config line is commented out, because the repo now has a new_study_prefix file in it.
If you have a dictionary called a, then passing **a into a function unpacks the dict so that all of the key-value pairs of the dict act as argname=argvalue pairs in the function call.   
You have to be confident that the function can take all of  those arguments, of course. But if a function declares **kwargs as its last argument, then that means "take any extra argname=argvalue pairs and put them in to a dict called kwargs.
See https://docs.python.org/2/tutorial/controlflow.html#keyword-arguments  and http://agiliq.com/blog/2012/06/understanding-args-and-kwargs/
passing around a dict using **a is a bit cryptic, but it is useful when you are writing an adaptor function. You can add keyword arguments to the delegated function and be able to use them without tweaking the adaptor.