fixed DirectoryNotFoundException if Mods folder did not exist, oops

fixed bug where audioclips would be pointlessly loaded multiple times
improved logging by removing unecessary details
multiple sound packs can be included per mod

Fixed bug where mod could crash when loading a betty with an empty folder

Changes:
- Fixes for unloading the mod
- All sound effects are now optional, sound effects not included in a voice pack will use a stock game sound instead

https://github.com/THE-GREAT-OVERLORD-OF-ALL-CHEESE/Custom-Sounds/issues/1
https://github.com/THE-GREAT-OVERLORD-OF-ALL-CHEESE/Custom-Sounds/issues/13

Ported from the VTOL VR modding website