Mediaplayer: remember position and volume

Change-Id: I43fa7cbcedd39c39e4b136e9e1f9bb34bf3eb570

MediaPlayer: Emulate duration attribute for BUrl playlists

* Make the Playlist window working again by caching
the duration value.

MediaPlayer: Add _CalculateDuration and archivable protocol

MediaPlayer: Avoid to recreate the supplier more than needed

* MediaPlayer attempted to recreate each time the media supplier(s),
and implictly it recreated also the BMediaFile. This works fine with
local data that can be accessed fastly, but makes lots of troubles
with network streams such as BMediaIO. The result of this was that
the Streamer plugin has been recreated each time having memory and
network wasted other than performances.
* I tried to keep intact the previous logic, and it looks OK for me,
this has been done by moving out of the Controller the ownership of
the TrackSupplier and adding a little utility class that do the
releasing job previously done by the ObjectDeleter.
* Reviews are appreciated.

Streaming: Remove any pointer BUrl argument

* There's no need to pass BUrl by pointer, this is
potentially dangerous and leaky without any advantage,
copying is definitely safer.

MediaPlayer: Add UrlPlaylistItem