libfaust reorganization and updates

[DBraun]

Bug fixes:

• In between renders, a plugin processor is now better told to turn off all MIDI notes. This is helpful if a render ends before a Note Off event.

Other updates:

• JUCE has been updated to 7.0.7
• Sampler Processor Plugin project has been updated.
• libfaust has been updated to 2.68.1
• libfaust (the Box and Signal API) files have been refactored into more isolated files
• The Faust Processor can now load soundfile primitives directly from the filesystem. If the file hasn't been specified via set_soundfiles then the filesystem will be checked.
• Python floats and ints can be implicitly converted into boxReal(val), boxInt(val), sigReal(val), and sigInt(val)

[DBraun]

Closing in favor of #176