Extensive refactor of the script + attempt to fix status reporting.

Items are now organized into 4 levels (owner - artist - fake entry - track), which made it possible to have correct "artist" and "title" data for tracks. This makes importing more easy and allows lyrics fetcher scripts to do their job.
Unfortunately, manual editing of tags after import is still required, since genre is set to track's owner and album is set to artist, but this is unavoidable (first - due to Amarok API limitations, second - due to Amarok scriptable service manager bug which makes it impossible to have empty album names).

I've also attempted to fix status reporting (URL structure changed in the meantime), but the corresponding methods somewhy ceased to be invoked (Amarok 2.8.0). Don't know why.