Added parent element to episodes.

You can now use episode.parent to reference the anime from within it.
This has been added so I can do episode name searches in the main app.
The name of the first Saki Nationals episode is "Saki: The Nationals Episode 1"
when watch "Saki: The Nationals" is called. Since the episode didn't hold any
information about the anime itself. I took the liberty to add a parent
element.

The parent element has to be supplied when the child is created. Unless the nokogiri element is a
tr, where the constructor can use the data supplied to figure out what anime the episode is connected to.