* Serialize broadcast_data within AsyncInfoController::base_data
Adds a `broadcast:` key to our `base_data`, regardless of whether a user is logged in or not.
If a broadcast is not present, passes along a `nil` value.
* Initialize active broadcast (if present) when rendering main page
* Allow admins to preview a broadcast's processed_html when editing
* Add some fixed position styling to active broadcast
* Add system specs around broadcasts on homepage
* Use sanitize in place of html_safe when previewing broadcast
* Do not initialize broadcast if no broadcastData available
* Render default value on broadcast in options_for_select
* JS cleanup
* Unset fixed positioning for static navbar config
Also add some default styling for an active broadcast
