Proposals/Support for multiple tags

Summary

ID3v2 and many other Tagging Systems allow Multiple Tags. Amarok ignores them. Users wish for mutliple Tags to be read & to be editable by Amarok.

Please discuss this proposal on its discussion page.

Try how TagLib Support looks - done, example file see tagtest.cpp Gist
Plan how to save multiple Tags in the XML File of the Collection Scanner - planning example: http://piratepad.net/QYDQn3Ardp
Change Collection Scanner to scan all the Multiple Tags and put them in the XML File
Plan how to save them in the Database
Change MetaTrack to return lists for genre and others. So instead of a GenrePtr genre() const; we should have GenreList genres() const;
Change Database. We would have a standard normalized database table layout. e.g. since Tracks<->Genre is a n:m relation we need a relation table. (change DatabaseUpdater)
Change Classes (SqlMeta, SqlRegistry and SqlRegistryPrivate) to handle the changed database layout.
Change the ScanManager to use all the new stuff.
Plan how to display multiple Tags in the UI
Change UI (CollectionBrowser, CurrentTrack Applet, Meta Data editor, Playlist items)

Start after 2.4.2 release
Use independent changes. E.g. changing the collection scanner XML but for a first step not using the information. Or returning GenreLists but for a first try just using the first entry, disregarding further genre results. This working mode allows us to always have a running Amarok and no need for a big merge when everything is done.
Work on a separate branch when we need to put all the parts together.