Artist search should honour COMPOSER/CONDUCTOR/BAND preferences

[stuarth]

At the moment the Lazy Search will match any kind of contributor when performing an artist search. The normal SlimServer search, however, is more restrictive in the following ways:

• I believe it may only search ARTIST, not ALBUMARTIST when finding tracks.
• It has behaviour settings to enable COMPOSER, CONDUCTOR and BAND to be treated as additional artists, and will ignore those kinds of contributors if not enabled.

The Lazy Search plugin should be consistent with that as it should return the same results (give or take the fuzziness you'd expect) as the standard search.

[stuarth]

Looking at how SlimServer works, I believe the tricks is to make use of Slim::Schema::artistOnlyRoles, which returns an array reference for the roles the user wants to consider as artists (taking the preferences into account).

See Slim::Schema::!ResultSet::Contributor::browse for an example of using this within a database search.

This should be used in the following areas:

1. When performing an artist lazy search, constrain returned contributors by the desired roles. Note that this
2. When lazifying the database for keywords, constrain the contributors for the track being lazified by the desired roles.
3. When pressing ADD/PLAY/INSERT on an artist name returned from a lazy search.

[stuarth]

I've implemented this in r189:190; it will be in the next formal release of the plugin. I've briefly tested it and it seems to work without upsetting anything.