Completed project from Mojca Božič - Elgar's "There is Sweet Music"

This was submitted by email as a response for a project status. Thanks Mojca!

The composers.dat file has been updated as has the projects.html-in file.

I moved the header section into a separate file (mutopia-header.ly). The mutopiainstrument field remains as original (S.S.A.A.T.T.B.B.) which, although accurate, might need to change to something in our instrument list (Voice?).