Add a dcloud_admin? method to accounts

Segregate organization_id == 1 check into Account instead of checking for in the controller.  This will better position code for when we break apart accounts from organizations.
Editing interface for featured reporting page

Convert the Featured Reporting page to source it's content from the database in markdown format.

To support this:
  * A Backbone editing interface is implemented at /admin/featured
  * Basic CSS to style markdown is included in pages/body.css   This may need to be tweaked to ensure desired styling.  A good test is to paste all the Markdown examples into a report and see how it appears.
  * Since the content is now pulled from the database, I've also added an RSS feed at /featured.rss
Retain user preferences on document embed dialog

Fix for issue #41.  Discovered that the preferences key was specified
incorrectly and the 'Link to original PDF' check-box wasn't being
restored.
Merge branch 'master' of https://github.com/documentcloud/documentcloud
Flagging changes to make to accounts when organization_id & role are extracted.
Setting up many to many mapping between account and organizations (while leaving existing belongs_to organization intact).
Extracting roles into a mixin.
shimming role helpers on accounts.
Merge branch 'master' of https://github.com/documentcloud/documentcloud
Merge branch 'master' into memberships
Adding some additional constraints around memberships.
Merge branch 'master' of https://github.com/documentcloud/documentcloud
Merge branch 'memberships' of https://github.com/documentcloud/documentcloud
Account Identities.

This adds a hstore column called 'identities' to the accounts.

When a account logs in using a third party login from omniauth:
* The column is searched for the omniauth provider's key and unique user_id
  * If found, the account is returned and stored in session
  * If not found, a new account is created, without a corresponding membership
Remove temp variable, set hash directly
OmniAuth provided identities

This provides the framework to load omniauth, initialize it and a
controller to handle setting up accounts from it
Bugfix for account not recording second identity login

On reflection I don't think other code should be able to update the
identity hash on an account directly.  Removed that method and also
the Account.new({profile_incomplete=>true }) bit that got in there
somehow.

As the code-base is right now, Rails throws an exception immediately on
logging in when it attempts to record the organization_id.  I'm
returning nil for right now to continue testing.
Add third-party login icons to sidebar on home page
DRY up route for identities
Migrations for roles and organizations shift data appropriately.