Added ActiveAdmin gem to the project, and run its installer.

This will be a foundation for an administration interface.
Separate active_admin JS and CSS files into discrete "admin" subfolders, so they are not loaded by the main feedbunch views.

This requires changing active_admin configuration so it finds the assets in their new locations.

Inspired by:

http://mrdanadams.com/2011/exclude-active-admin-js-css-rails/
Added ActiveAdmin route to routes.rb

Not yet implemented: authorization-filtered access to the activeadmin route.
Added Feed resource to ActiveAdmin.
Minor change in config.
Resque web interface is now accessed at /resque path, instead of /admin/resque.

This is to avoid possible clashes with the ActiveAdmin interface.
ActiveAdmin web interface is accessible in the /admin path only for users with admin attribute set to true.
Removed acceptance test that always fails if run without a Redis instance present.

Our CI environment does not have a Redis instance running.
Added link to ActiveAdmin web interface in the user dropdown.

This link is only visible for users with the admin attribute set to true.
Customized ActiveAdmin views for Feeds and Users.
Folders belonging to a User can be browsed and edited with ActiveAdmin.
Added multi-selectable column to ActiveAdmin views, to enable batch actions on resources.
Added table with subscribed feeds to the user show view in ActiveAdmin.

I'm still not too happy with it.
WIP: display useful information in ActiveAdmin views.

Now the user show view displays, below the user attributes, two tables:

- Folders owned by the user
- Feeds subscribed by the user

Also useful information which is not a database column, like number of feeds in a folder, number of unread entries in a feed for the selected user etc are displayed. Each table row has a "View" link which goes to the individual feed or folder show view.

To enable this change some ActiveAdmin views are rendered with partials (files with .builder extension in app/views/admin subfolders) instead of configuring the view in the ActiveAdmin resource definition (files under /app/admin).

The change to partials has been inspired by this StackOverflow post:

http://stackoverflow.com/questions/13422751/rails-activeadmin-showing-table-of-a-related-resource-in-the-same-view
Added breakpoint to better separate comments in the user show view in ActiveAdmin.
User index view in ActiveAdmin is rendered with a partial, instead of being part of the ActiveAdmin resource config.
In ActiveAdmin the folder show view displays a table of feeds in the folder.
Feeds displayed in the feed show view in ActiveAdmin, have a link to their folder show view if they are in a folder.
Removed unnecessary try calls.
Feed show view in ActiveAdmin is rendered with a partial, instead of being part of the ActiveAdmin resource config.