All enabled tests are now true unit tests with no external dependencies; new `requirements.txt` file in `test/` that installs testing requirements (`pytest`, `pytest-mock`, etc.); and `run-tests.sh` now has an extra step that installs these

All enabled tests now pass. TODO: Refactor integration tests into unit tests; add more test coverage

system since I figure that's on its way out the door)

updated WorkflowEvent shape

wf_monitor to use new amqp_helpers setup; updated wf_monitor tests;
updated WorkflowEventSchema to accept a string in the timestamp field
instead of a datetime (we could probably change this, but this is how
it's set up for now)

originally going to use a singleton pattern but ran into issues with
that)

Hopefully final changes to setup.py files regarding package name changes; renamed a amqp_helpers dir to channels

Made amqp_helpers directory structure match the other subprojects. Made some small changes to monitor.py and test_monitor.py

Added __str__ and __repr__ methods to WorkflowMonitor; small updates to same methods in WorkflowEvent