Update to instruments.xml

Added common genre tag to Acoustic Bass
Merge pull request #498 from ChurchOrganist/Instruments.xml-update

Update to instruments.xml
make plugin manager persistent
In French kbd, shortcut for adding a rest to TAB conflicts with shortcut for fret 4.

Fixed by changing the former to ';'
Merge pull request #500 from mgavioli/Fix_TAB_rest_shortcut_for_French_kbd

TAB shortcut conflicts in French kbd