Use Sequel.ilike, not :sym.ilike, in Episode::by_slug
Make by_slug return the first result
Eagerly load playlist track details from Episode
Find presenter from synopsis if missing in title

This seems to only apply to Late Junction Sessions, where the title
contains the names of the artists collaborating, not the presenter.
<http://www.bbc.co.uk/programmes/b026rjh5> is one example.
Add Episode#title_date
Add #slug and ::by_slug for Presenter
Sort playlist tracks by time, if available; ID otherwise
Eager load associations graph for playlist items