Review request: MemoryMeta changes and new iPod collection

[Matěj Laitl]

Hi list and mainly Bart,
please review memorymeta-tweaks branch [1] in my personal git clone which 
contains changes that I needed for iPod collection rewrite.

[1] 
http://quickgit.kde.org/?p=clones%2Famarok%2Flaitl%2Famarok.git&a=shortlog&h=refs/heads/memorymeta-
tweaks

UmsCollection would get support for following for free is memorymeta-tweaks is 
merged:
 * album artists (was hard-coded to track artists previously)
 * less memory leaks due to circular referencing removal
 * capability forwarding: editing tags thanks to EditCapability.

ChangeLog is added for above entries.

With a small bit of work, UmsCollection could get support for:
 * album covers if MetaFile::FileAlbum::{image(),hasImage()} is implemented
 * compilations if MetaFile::FileAlbum::isCompilation() is implemented (see 
ArtistHelper::bestGuessAlbumArtist())
 * track removing reflected in collection browser, call 
MapChanger::removeTrack() perhaps somewhere in 
UmsCollectionLocation::removeUrlsFromCollection()
 * track metadata changes reflected in collection browser if you observe tracks 
in UmsCollection and then call MapChanger::trackChanged() in 
metadataChanged(). You should emit updated() when trackChanged() returns true. 
Beware that it cannot currently cope with changes to track uidUrl().

ChangeLog is not updated with above entries as the changes are not user-
visible anywhere in Amarok yet.

All of the MemoryMeta changes are already used & tested in iPod collection 
rewrite that can be found in the ipod-rewrite branch [2], which is nearly 
merge-ready.

[2] 
http://quickgit.kde.org/?p=clones%2Famarok%2Flaitl%2Famarok.git&a=shortlog&h=refs/heads/ipod-
rewrite

Regards,
			Matěj Laitl