feat: Docker support for mysql

- Docker now will use a mysql image
- base.py now loads mysql as the default database
with configuration env vars
- Also remove postgres remnants

Signed-off-by: David Haynes <dhaynes3@gmu.edu>
3 jobs for 32-mysql-move in 20 seconds
Name Stage Failure
failed
whats-open-py2.7 Test There is an unknown failure, please try again
    __import__(name)
File "/builds/srct/whats-open/whats_open/whats_open/settings/local.py", line 5, in <module>
from .base import *
File "/builds/srct/whats-open/whats_open/whats_open/settings/base.py", line 133, in <module>
'NAME': os.environ['WOPEN_DB_NAME'],
File "/usr/local/lib/python2.7/UserDict.py", line 40, in __getitem__
raise KeyError(key)
KeyError: 'WOPEN_DB_NAME'
ERROR: Build failed: exit code 1
failed
whats-open-py3.5 Test There is an unknown failure, please try again
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
File "/builds/srct/whats-open/whats_open/whats_open/settings/local.py", line 5, in <module>
from .base import *
File "/builds/srct/whats-open/whats_open/whats_open/settings/base.py", line 133, in <module>
'NAME': os.environ['WOPEN_DB_NAME'],
File "/usr/local/lib/python3.5/os.py", line 725, in __getitem__
raise KeyError(key) from None
KeyError: 'WOPEN_DB_NAME'
ERROR: Build failed: exit code 1
failed
whats-open-py3.6 Test There is an unknown failure, please try again
  File "<frozen importlib._bootstrap>", line 205, in _call_with_frames_removed
File "/builds/srct/whats-open/whats_open/whats_open/settings/local.py", line 5, in <module>
from .base import *
File "/builds/srct/whats-open/whats_open/whats_open/settings/base.py", line 133, in <module>
'NAME': os.environ['WOPEN_DB_NAME'],
File "/usr/local/lib/python3.6/os.py", line 669, in __getitem__
raise KeyError(key) from None
KeyError: 'WOPEN_DB_NAME'
ERROR: Build failed: exit code 1