Refactor settings files

The current way settings work, they set a bunch of things and
then try to import local_settings.py, which means local_settings.py
cannot modify anything set in the importing file; it has to
completely override it.

These changes make local_settings.py the top-level file, which needs
to be created before anything will work. It should import any of a
number of environment-specific settings files (dev, staging, test,
production) and can then override anything it needs to.
DB settings in base; move local with others

* Add default database settings to pycon/settings/base.py
* Move local settings to pycon/settings/local.py
Merge branch 'develop' into feature/78-refactor-settings
Update settings to get server values from environment
Merge branch 'develop' into feature/78-refactor-settings
Bool in env will be 'true' or 'false'
Merge branch 'develop' into feature/78-refactor-settings
Merge branch 'develop' into feature/78-refactor-settings
Cleanup, comments, tweaks
Merge branch 'feature/78-refactor-settings' into staging