Change generate_output to bulk upload blank events
Add --bulk-send-blanks flag

In addition to the new flag, I retained support for using --skip-blanks
to retain backwards compatibility. If --skip-blanks is specified, the
new flag has no affect.

Also, I extracted out the REDCap records creation to (hopefully) explain
what was happening with the `defaultdict` and merging form data into
records.
Fix docstring indentation
Merge branch 'bulk-send-blanks' of https://github.com/ufl-taeber/redi into develop

Conflicts:
	redi/utils/throttle.py