Integrated permission model and some cancan abilities as a starting point.
Merge branch 'master' into permissions

Conflicts:
	db/schema.rb
Somehow working but surely incomplete authorization.
Repaired admin controller tests.
Merge branch 'master' into permissions
Tried ability config for Version.
Merge branch 'master' into permissions
A little better rights management.

* Show only managable domains.
* (^-- also in #new and #edit)
* Show 'Changes' menu only for admins.

Caution:
On 'not managable' domains, #index does still work!
Merge branch 'master' into permissions
Combined admin/aliases and admin/mailboxes controllers and wrote functional tests for both.
TODO file.
TODO: Make encrypted_password editable.
TODO: Login logging?
TODO: 500 in versions index.
TODO: Exception for 500 on versions index.
TODO: Better display of deleted items in versions index.
Changed AliasesAndMailboxController to make use of handy inherited resources methods and saved some lines.
Merge branch 'master' into permissions

Conflicts:
	app/controllers/admin/aliases_controller.rb
	app/controllers/admin/mailboxes_controller.rb
Added quick mailbox login session switcher in development mode.
More mature authorization.

* Opaque session switcher in development mode.
* Roles and permission list on mailboxes#edit.
* Correct nestind authorization of domains and associated mailboxes and aliases.
* Do not show delete buttons, if not authorized to delete.