Add active admin into the application
Make the petitions default to the constant if nothing is set
Overload the create method for the admin interface to avoid any session specific info being required

Since we are using a different auth system for the admin we can't reuse all the code for the admin
interface, and we shouldn't so using the overloading provided by ActiveAdmin we override the defaults
at the controller level for petition and can create them directly from the admin dashboard.

The same will need to be done for most models. And that's a good thing.
Merge branch 'master' of github.com:brianto/civic-app-petition-prototype

Merging the active admin and master changes
Fix issue with styles, you don't need to require the tree at application.css
Fix the pagination centering