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
Adding some design tweaks to Financial Aid review pages.
Doc and comments
Rename README to README.rst
README formatting
Use settings from env by default in base settings
Tweak docs based on testing
Re-enable social auth

For #114.
Merge pull request #190 from caktus/financial-aid-design

Financial aid design layout changes.
Handle existing account better

* Raise the right exception when someone tries to sign in from
  an unassociated auth provider using an email that already has
  a PyCon account
* Use the social_auth middleware that catches such exceptions, goes
  to a page you've chosen, and displays a useful message.
Don't overwrite User.email on association

When I associated my yahoo account, it changed my email to
my Yahoo email in User.  Add a django-social-auth setting to
tell it not to do that.
Go back to finaid application list after submitting review changes

For #192