Problem: can't use custom soundfont with loaded midi

[Aleksey Malevaniy]

Pianobooster works well even for custom soundfonts choosen from Qsynth. But! When you load midi-file for learning, pianobooster allows to use instruments from standart fluidsynth soundfont FluidR3_GM only and to get back to playing custom soundfont I have to remove .config/Pianobooster. So one can't learn with pianobooster and custom soundfont.

Custom Soundfonts can significantly improve how it sounds, get it closer to real piano, so it would be great to solve this problem. Thanks!

[romul]

Forwarded https://github.com/captnfab/PianoBooster/issues/65