Hydrogen-1.2.1 patch release

This patch release fixes a number of bugs and inconsistencies found in version 1.2.0.

Changes

• Update French translation

Fixes

• Fix reopening of last used Playlist. In addition, in case the
  PlaylistDialog was opened at the end of the last session - when
  "Reopen last used playlist" is checked in the Preferences - the
  dialog will be reopened too at the same position.
• Fix spurious marking of opened songs as modified.
• Fix MIDI (output) feedback for metronome toggling and pan
  setting.
• Fix superfluous MIDI event - Action bindings. An incoming MIDI
  event can be mapped to an Action only once.
• Fix tool tips of MIDI-learnable widgets. All bounded MIDI events
  will be shown.
• Fix MIDI note output for channel 16 (previously only channel
  1-15 were accessible in the InstrumentEditor).
• Fix spurious tempo changes to 120bpm when switching songs or
  between pattern and song mode (#1779 and #1785)
• Support "START", "CONTINUE", and "STOP" type System Realtime
  MIDI messages in PortMidi and CoreMidi.
• Fix MIDI action binding to incoming MMC_DEFERRED_PLAY event.
• Fix missing MIDI driver restart when adjusting corresponding
  parameters in Preferences.
• Fix MIDI Machine Control (MMC) event type handling on Windows
  (#1773)
• Fix loading of legacy drumkits. All layers but the first one
  were dropped during drumkit upgrade (#1759)
• Fix MIDI input handling with "Discard MIDI messages after action
  has been triggered" checked. Incoming NOTEON message were
  dropped without triggering a sound (#1751)
• Fix beat and bar calculation in pattern mode (#1741)
• Fix compilation in GCC with -Werror=format-security (#1739)
• Explicit usage of Python3 in stats.py script
• Fix build against Musl (nekopsykose)