Gdctools

. gdc_miror now longer exposes --date CLI arg; it was never relevant because
the mirror creates datestamps
. rest of tools more intelligently infer correct datestamp to use
. gdc_loadfile now exposes --format arg, to choose between FireCloud/Firehose
and generates case (participant/donor/individual) loadfiles in firecloud mode

. Corrected file paths in files generated by gdc_loadfile

. Misc tweaks arising from OPS testing

. Major step forward in rationalizing interplay of CLI args and config files
. Including definition of scopes, specificty & precedence in GDCtool.py
. Tweaked some of the tests to demonstrate & test this interplay
. Updated a few more baseline test datafiles that had lingering V6 content

. Changed paginated queries to begin at page=0 instead of page=1;
. apparently in v1.9.0 the GDC API changed from 1-based to 0-based indexing?

. Re-establish usability with BOTH Python 2 and 3
. Motivated by contributions from https://github.com/aswanipranjal