Re-work MPRIS2 support

Using Eike Hein's setup, which is easier to maintain.
MPRIS2: Give out full-size cover images if possible
MPRIS2: Make sure Seeked is emitted when track position decreases

It is no use just emitting it during the trackChanged signal, as it is
possible that the position has not been updated at this point.
MemoryMeta: support for propagating album image updates

...also modify refreshing algorithm when one track from an album is
updated to always report correct isCompilation, canUpdateCompilation,
image, hasImage, canUpdate image flags. Previously it was impossible
to unset cover image for an album for example.
IpodCollection: support for writing album covers to iPods

FEATURES:
 * Support for setting and unsetting cover images for iPod albums, can
   write back covers to file meta-data too, respects configuration.

DIGEST: Feature
IpodCollection: move all actions from playlist provider to collection

The actions are however all mirrored in playlist provider. This is to
make the stale & orphaned action more conveniently accessible (without
having to go to Saved Playlists)
IpodCollectionFactory: the iPhone change landed in kdelibs 4.8.3

...update the messages then.
MetaFile::Album: support for setting album cover and common album actions

FEATURES:
 * Support for setting cover images for albums on USB Mass Storage devices.

DIGEST: Feature
CollectionLocation: remove deprecated remove() from the top level

It is removed from subclasses that don't call it, too. Some of them use
the method internally, these declarations are changed to be non-virtual.
CollectionLocation: deprecate insert() further, remove unused implementations
SqlCollectionLocation: preserve statistics in copyUrlsToCollection()

CHANGES:
 * Preserve statistics when copying or moving tracks to Local Collection.

DIGEST: Bugfix: Amarok now preserves track statistics during copy
QtGroupingProxy: don't re-enter beginInsertRows() (crashfix)

This should fix a nasty crash that was only reproducible when Qt was
build with debugging assertions enabled. (and perhaps only if you have
empty playlist providers) The fix is based on an assumption that
addSourceRow() in QtGroupingProxy is only called from:

a) buildTree(), which encompasses it in {begin/end}ResetModel()
b) modelRowsInserted(), but that should be always preceeded by
   modelRowsAboutToBeInserted() that calls beginInsertRows()

Bart, this is largely your code, is this correct?

BUGFIXES:
 * Fix crash on start when Qt is build with debugging assertions

BUG: 285720
FIXED-IN: 2.6
DIGEST: fix rather nasty crash
TranscodingJob: fix transcoding with ffmpeg >= 0.10

BUGFIXES:
 * Fix transcoding with ffmpeg >= 0.10; patch by Julian Simioni.

FIXED-IN: 2.6
REVIEW: 104839
DIGEST: bugfix
SqlCollectionLocation: re-read bitrate, length, samplerate.. when transcoding

This was not a huge problem as the re-read is triggered on first file
change or full rescan, but this way we have the fields correct from
start.
IpodCollection: small fixes to signals and slots
UmsCollection: when tracks are changed, update collection more promptly

This is a rip-off of commit 7a8edcd8dffb6d682e19ea4b5738cf939dee1267
applied to IpodCollection.
Amazon store: ability to check single items out directly

So the user does not have to use the integrated shopping cart (which
does not work for Amazon.com at all, due to their API limitations).
This currenly only works correctly for Amazon.com, some server side
changes are required for the other locales. Those will show up shortly.

BUG:288808
FIXED-IN:2.6
Playlist::Controller: fix behaviour on append ̛& play with random progression

...we now choose one random track from the inserted ones and start
playing it. Also, fix a bug where Amarok would start playlist added
songs even if all of them are filtered.
UserPlaylistProvider: set object name so that del key works

CHANGES:
 * Make delete key work in Saved Playlists.

DIGEST: bugfix
CollectionTreeView: clean up, no functional change