Use the envvar FLASKTODO_CONFIG to load config

The app will now load configuration from the Python file referenced by
the environment variable 'FLASKTODO_CONFIG'. If this variable is not
defined or the file is not found, do nothing.
All uppercase attributes from the file are loaded, other attributes are
ignored.
Deploying the app with Fabric
Ignore the Fabric's configuration file: fabconf.py
Use POST (instead of GET) to modify tasks state