Add authorization for channels; initial implementation is such that only administrators may delete channels. (refs #131, #154)
Don't render delete button unless channel metadata contains trueish destroyable flage.
Introduce channel ownership; delete button only displayed for destroyable channels (non-primary, owned, or all except primary channel if you're an admin).
Channels now need a user.
Remove obsolete additional attribute for channel JSON.
Add users_controller and set as show/index resource in routes.
fix abilities for channel ownership
Better user handling; better initialization callbacks.
Merge branch 'kandan-131'

Conflicts:
	app/assets/javascripts/backbone/kandan.js.coffee
	app/assets/javascripts/backbone/views/channel_pane.js.coffee
	app/models/ability.rb
	spec/factories/channel_factory.rb
Increase capybara wait time to 10s for locating .chat-input.