Trakt.TV Account Login Authentication

When inputting your Trakt.tv account credentials DuckieTV now checks to see if the credentials are valid.

Sends a simple HTTP Post request to `http://api.trakt.tv/account/test/apikey` and either returns a `success` or `failure`.
If `success` continues to save credentials however if `failure` (or anything !success to be more specific) it will not save anything and display an error to the user specifiying incorrect User / Pass or that Trakt.tv might be down.

Still needs proper translation keys

Still needs proper handing for when trakt.tv returns an >500 error which Schizo said he'd do.

This literally took me hours to make trying to find a bug that prevented this working :(

#249