Issue #64: Don't display menu items not supported.

Photos and Music are not supported so don't display those menu items
currently.
Issue #57: Implement and update DownDroid for managing downloads.

The new download manager will be based off code from the DownDroid project.
Issue #57: Replace Existing DownloadManager Service

Replaced the built in service with a new one built off the DownDroid projects
source code. This was modified so that it could handle files larger than
2gb, reads in 8k chunks instead of 1K, and accepts a destination directory
and user defined filename.

Items still to complete.
* Viewing the Queued downloads and progress.
* Better Notification integration.
* Canceling the downloads.
* pausing and resuming the downloads.
Issue #62: Add Help Tutorial

Adds a Help Tutorial to the application that gives an overview of Serenity
for Google TV and it's functionality.