Python3 swarm

Python Requirements Update

Add Studio note about mktg site delay

BOM-630

python3 compatibility

BOM-484

BOM-432

REST API docs

Add a note when marketing site is enabled that there is a delay
from changes in Studio appearing on the marketing site.

DISCO-1356

We updated the underlying methods to always be passing unicode strings
aronud and only encode them to bytes when we need to hash them.

Python 3 changed how rounding is performed. In Python 2, .625 rounded to
.63 (as our grading code rounds it, so the test passed).  In Python 3,
.625 rounds to .62.  This fixes the test by avoiding round() to
calculate the expected value, and instead simply using the value we
expect.

The django test client returns bytes, and many of our tests start using
it like a string. This was fine in python 2 but not in python3.

Update the tests around static_file code to use byte streams instead of
string streams for generating static content.  This is a fix to get
these tests passing on python 3.