Initial implementation of authorization adapter
Added authorization to Pages
Started on the CanCan adapater
Added tests and docs
Fix error message
show scopes even if no results are found

When using filters, the previous behavior was to hide all scopes. This
is counterintuitive, as a different scope from the current one may have
results for the selected filter, and ends up confusing the user.
add conditional :if and :unless logic to filters

+ followed the way conditional procs are built for Scopes
+ by way of Array.group_by, we now only recognize the last-defined
  `filter` call for each individual attribute
+ update the specs to allow `filter` to be called multiple times on
  the same pseudo-document
Fix conflict with Redcloth
Added powered by translation
routing fixed for Devise on root namespace
allow custom CSS class for rows in attributes_table
Fix typo
Added missing batch actions translations leading to no labels (see PR #1788)
Merge pull request #1814 from EtienneDepaulis/missing_batch_actions_translations

Added missing batch actions translations leading to no labels (see PR #1788)
Merge pull request #1807 from adrienkohlbecker/master

Fix #1805 conflict with Redcloth
Update CHANGELOG
Merge pull request #1810 from kieranklaassen/patch-1

Added powered by translation
Fix fields_for_params when Boolean values
authorization_adapter documentation additions
Added #normalized to help in simple matching in auth adapters.

The `#authorized?` method's subject can be set to both instances as well
as classes of objects. This can make it much difficult to create simple
case statements for authorization since you have to handle both the
class level match and the instance level match.

For example:

    class MyAuthAdapter < ActiveAdmin::AuthorizationAdapter

      def authorized?(action, subject = nil)
        case subject
        when Post
          true
        when Class
          if subject == Post
            true
          end
        end
      end

    end

To handle this, the normalized method takes care of returning a lambda
which implements `===` to be matched in a case statement.

The above now becomes:

    class MyAuthAdapter < ActiveAdmin::AuthorizationAdapter

      def authorized?(action, subject = nil)
        case subject
        when normalized(Post)
          true
        end
      end

    end