Modify loadAnimated to enable simpler calls to scrollToTop

We may need to scroll to the top of the page from anywhere, so this
moves that part into its own little helper and calls it from there
instead. Not a massive difference, but hey ho.
Ajaxify channel playlists

Removes playlists code from the ChannelController and adds a new
method to the PlaylistController instead. This is then called by
Ajax and loaded into the appropriate tab.

Currently this acts on click, which IMHO is shit. This needs
to happen automatically or it's pointless. Probably do some
work on the wrapper package to support the calls there directly.