Tuning override of global 'note 0' reference

[j5v]

As a user, I work with multiple tunings with different reference frequencies, and want this reflected in analysis, and displayed above each overridden tuning row at the appropriate point on the tuning line. I need an optional reference frequency in each tuning, to override the global reference, and want to edit this in Tuning properties.

Follows from #23.
'Could-do' because fewer users need this.