Update instruments.xml to add new families and improve sorting

Run share/instruments/update_instruments_xml.py to fetch the latest
version of the online spreadsheet. In this version, every instrument
has been assigned a family. Also, instruments are now sorted based on
their group, family and minimum professional pitch, among other things.
This ensures they appear roughly in score order according to standard
orchestral layout. Finally, descriptions have been improved and a few
small fixed made to fix incorrect or missing data.

In addition, some compatibility code was changed to improve instrument
recognition in older MSCX score files that lack the appropriate
MuseScore or MusicXML instrument IDs. The old code returned the *first*
instrument that matched a given criteria (e.g. same trackName), whereas
the new code returns the instrument that gives the *best* match
according to multiple criteria. This means the return value is less
dependent on the order in which instruments are defined within
instruments.xml.