* Show the timer when playing
 * Fix the track index loading on saving/restoring synth state
 * Clean everything on delete

This patch adds a new view to the application to show the MusicGrid for
each track.

There's a python binding library and it's better to use it directly
instead of create a new binding using the socket API.

This binding is really small, so instead of adding a new dependency,
this patch adds the fluidsynth.py file that's copied from
https://github.com/nwhitehead/pyfluidsynth

This patch also simplifies the Synth class interface.

Add the scale and number of rows widgets to be able to customize the
MusicGrid.

Based on https://music-grid.surge.sh/

This patch adds the keypress/keyrelese event management to the keyboard
so each key in the MIDI keyboard is "played" with a keyboard key.

The key mapping is not ordered with the QWERTY layout so a possible
improvement could be to create the map in a configuration python dict so
it could be changed in the future, depending on the user keyboard layout
or preferences.

We'll use the  fluidsynth to create a custom software keyboard to be
able to compose music without instruments, just a computer keyboard or a
mouse.

This will make the app looks almost good on dark theme.