Some python3 changes

[asottile]

Just some quick changes before I had to run off to other things:

• Adds a py3 tox env, it doesn't pass yet but it can at least be attempted
• Change basepython to use /usr/bin/... syntax, this allows environments to be recreated while active
• The py3 environment can successfully build, but not yet pass the tests (before it wasn't even installing correctly)
• Remove dep on importlib, paasta wasn't actually using anything that wasn't in python2.7 anyway (and it also wasn't necessary, __import__ sufficed)
• Change a single unicode -> six.text_type: started to fix tests
• Upgrade python-daemon to get python3 support
• Remove wsgiref, this has been in the stdlib since python2.5
• Remove argparse, this has been in the stdlib since python2.7
• Remove functools32, this isn't imported
• Use str('') for native string literals in setup.py to appease setuptools

[asottile]

make itest_lucid passes

$ make itest_lucid
Everything worked!
Everything worked!
make[1]: Leaving directory `/nail/home/asottile/trees/paasta/yelp_package'

[solarkennedy]

This is massive. Thank you very much! Especially for the contextlib.nested and stringio stuff :(