Composer final (piece 90 change, BourgeoisL)

As discussed by email, this fixes piece 90 so that the piece is composed by Loys Bourgeois. There was no existing moreinfo field with an attribution although one appears in the RDF; when this is processed that field will go away.

The composer BourgeoisL is added to composers and this pieced is moved to that folder.

Note that the inscriber's composer field is set to 'Genevan Psalter, 1551' which is actually a reference to a collection. This was left as is and I modified mutopiacomposer, respecting the  inscriber's possible wish that that name appear on the sheet music.