Add Balalaika Family to Instrument List

A response to this thread http://musescore.org/en/node/27581 but the
balalaika family was also asked for in 2012:
http://musescore.org/en/node/15908. A little digging this morning
enabled me to find the requisite string data. Not sure I have the clefs
correct though these are pure speculation in the absence of information
from the web
Merge pull request #1038 from ChurchOrganist/Add-Balalaika

Add Balalaika Family to Instrument List