Recursively search preset directories

[helgoboss]

This would be nice for being able to take presets from different sources as symlinks, e.g. Dropbox etc.

Not sure if we should apply name-spacing (applying the relative directory names as part of the preset ID). I think JSFX does it that way. Could be nice to also resolve naming conflicts elegantly and would probably be consequent since we already use the file name as a preset ID. It would also mean though that moving stuff into another directory would invalidate preset references in existing projects. Maybe we could use a fallback strategy and ignore the directory part of the preset ID if we don't find it there.

[helgoboss]

• Sub folders are now supported
• Sub folders in sub folders not (disabled intentionally at the moment)
• Preset ID will contain the folder name
• No fallback is applied (if the folder name doesn't match). It needs to be a strict match.