Pot preview recorder: Allow recording preset previews for exporting purposes

[helgoboss]

with preset names as file names and custom output format

[helgoboss]

Implemented in bb2171b

[helgoboss]

I've implemented this in the following way:

• The output directory is actually not configurable. It's always $DOCUMENTS_DIR/Helgobox/SoundPot/Preview Exports/$DATE_OF_EXPORT
• Within that directory, the presets will end up in the following structure: $PLUGIN_NAME/$PRESET_NAME.$EXT
• The way SoundPot renders the previews is completely customizable (audio format, normalization, MIDI note, ...). Because it uses an export RPP file that you can adjust before rendering. SoundPot will tell you about this prior to the first export.
• SoundPot will not check if it already rendered some previews, it will always render all previews in the list. It creates a completely new export directory for each export, so it can never overwrite existing files between two export sessions.