Merge branch strohel-for-2.6 into master

This merge was agreed on the mailing list, so push it.

* strohel-for-2.6: (21 commits)
media device collections are never organizable: remove a bunch of cruft
media device handlers: minor cleanups
media device collection: implement batch meta-data changes in EditCapability
media device collection: factor out EditCapabilityMediaDevice to its file
iPod collection: convert from ReplayGain to Sound Check and vice versa
media device collection: whitespace fixes
media device collection: merge WriteCapabilityBase and WriteCapability
media device collection: merge ReadCapabilityBase and ReadCapability
media device collection: get rid of CustomReadCapability - was unused
Collection browser: show absolute free space on hover, thicker bar
{media device,ipod} collection: remove unused writeDatabase() method
media device collection: more consistent handling of compilations
Get rid of UpdateCapability entirely - it was no longer used
collection location: remove UpdateCapability use from slotFinishRemove()
current track applet: remove historic cruft (UpdateCapability use)
iPod handler: remove duplicate function call
MediaDeviceArtist::albums() is not used, do not maintain album list
Media device handler: remove debug stamps, not useful anymore
playlist: show also albumArtist, BPM, labels, lastPlayed and bitrate in tooltip
iPod handler: raise libgpod dep to 0.7.93 and simplify iTunes db writing
remove IpodHandler::slotInitializeIpod(), it was not used anywhere