Support HTTP Basic Authentication for Feeds

Enables the use of feed URLs with the format http://user:password@example.com
Added single purpose app integration

Antennapod will now import subscriptions from AntennaPodSP (https://github.com/danieloeh/AntennaPodSP) forks when launched
Merge branch 'BasicAuth' of git://github.com/cszucko/AntennaPod into cszucko-BasicAuth
Added username and password to preferences
Added authentication support to DownloadRequester and HttpDownloader
Added authentication notification
Implemented DownloadAuthenticationActivity
Added authentication dialog to OnlineFeedViewActivity
Improved layout of AddFeedActivity

Confirm-button was moved up because it actually belongs to the 'Add podcast by URL' section.
Don't encode already encoded URLs. fixes #376
Playback was not completed correctly. Might fix issue #366 and #374
Prevent images from being loaded multiple times

(copied from AntennaPodSP)
Added support for images in itunes:image tags.
PlaybackPreferences were not written correctly when a playback error occurred (issue #374)
Prepared release of version 0.9.8.3
Added presto client dependency as source code
Added licenses to about-page
Fixed database upgrade to version 12
Navigation bar icons in audio player were not displayed correctly
Updated translations, added Hebrew translation