Bump version to 3.0.7 to handle portamento legacy
Prior to this version, mono and legato modes always had auto
portamento (i.e. portamento only happened when notes were
played legato), and poly mode never had it (i.e. when portamento
was enabled, every note had portamento regardless of playing
style). Since the introduction of the new auto portamento mode
parameter, where the necessity to play legato is now governed by an
explicit parameter, we need to potentially set this parameter when
loading older files so that the portamento behavior remains the same
as originally intended.