Default host to localhost when in development mode.

* Running Rack apps on 0.0.0.0 in development mode will allow malicious
  users on the local network (ex: Coffee Shop) to abuse or potentially
  exploit the app. Safer to default host to localhost when in development
  mode.
Merge pull request #1052 from postmodern/localhost_development

Default host to localhost when in development mode.
Merge remote-tracking branch 'upstream/master' into super-admin