Implemented Survivor metric

    Not ready for review yet.

    Implemented survivor backend for metric described in Mingle card 701.
    Added test for Survivor metric.
    Implementation is pretty much done.
    Right now designing tests.
    Refactored pages_created tests and refactored survivors test data
        creation in fixtures.py
    Updated queries, Finished writing tests.
    Added scripts/debug.py script to use with ipython.
    Added more tests.
    Flake8 passes

Change-Id: I12a65b71802f27074bfc4920c402215627d2e6eb
Merge branch 'master' into HEAD

Conflicts:
	tests/fixtures.py

Change-Id: I5ae8cd9339a1ab62d847589ed5cb835820cb12f9