Drag n drop flac files

[d.healey]

Currently it's not possible to drag n drop flac files onto the mapping editor, but you can load them through the import samples dialog. Could you add the ability to drag n drop them too?

[LightandSound]

@d-healey https://github.com/LightandSound/HISE-Stage/blob/d44b6d912390820c0b49e0dbb73e09c1d03ca83c/hi_tools/hi_standalone_components/SampleDisplayComponent.cpp#L392

register FLAC in the audio format manager and you're done