Synthesizer modernization

[Danielku15]

For a long time we have been using a port of TinySoundFont as a core for the SoundFont synthesizer.

While it fits exactly our needs, it lacks of some functionalities which cause problems during playback with newer soundfonts like the freely available MuseScore SF3 files.

As part of this issue we look into modernizing/extending the synth core to:

1. Ship a higher quality soundfont with alphaTab without (significantly) increasing the package size
2. Extracting the main soundfont into an own package to reduce the core alphaTab package size (only publish nightly if changed).
3. Improving the synth engine to sound "correct". (check for general bugs and add support for modulators).