Backup and restore feed list

Use the Backup API to backup and restore the list of feed subscriptions,
i.e. the OPML file.
Restore subscriptions when the app is first started

Perform a subscription list restore when the app is started for the
first time. Use a preference setting to figure out if the app is freshly
installed or not.
Allow restore from any AntennaPod version
Restore happens by itself upon app install
Added feed generators, basic rss tests
Disabled downloading of episode images. closes #390

Uses too much bandwidth
Added navigation drawer + new episodes fragment
Added secondary button to new episodes list
Added queue fragment
Added downloads fragment
Disabled downloading of episode images. closes #390

Uses too much bandwidth
Merge branch 'backup' of git://github.com/liesen/AntennaPod into liesen-backup

Conflicts:
	src/de/danoeh/antennapod/activity/MainActivity.java

Moved calls to BackupManager from PodDBAdapter to DBWriter
Changed backup API key

Now using key for 'de.danoeh.antennapod' instead of 'de.danoeh.antennapod.debug'
Added playback history fragment
Sorting via drag and drop was interrupted by download observer
Added fragment for adding new podcasts
Reimplemented ItemlistFragment
Added action button functionality
Added FeedItem dialog
Improved external player layout