Private Tracker Support for hdbits.org

These changes add support for the private tracker hdbits.org. A few notes on implementation:

* The code requests the login form itself before actually logging in. The login form has a changing hidden field that is required when posting login credentials.
* Parsing is done via regex. This should be somewhat flexible but could break if the page layout changes. The site layout has not changed in several years though.
* I added a toast notification when the user's username/password combo is wrong. Without this toast the user is simply told "no search results". Once better feedback is given in the main app this toast should be removed from this adapter.
* It's not included here but an IMDb or TVDb ID could be easily retrieved for torrents in the list as well. Combined with themoviedb.org or thetvdb.com this could be used to create a media rich search results UI. Something to think about.
* So long as I continue to use hdbits and Transdroid I would be happy to maintain this class if/when the site changes.