Hey,
I've downloaded demo version and in VISUALS tab I have empty spaces instead of library of shapes.
I'm running macOS 10.12.6
You can att he moment add custom particles clicking on "sprite" button on the right to select one of the visuals have to appear there.
The problem was hard to solve due we wanted to people add custom folders with their particles, but due Mac filesystem was unable to do it right, so we changed and we gonna add that images inside the app no folders so can be acceses via Mac with no problem.
Sorry for delay, hope to release the new version with this and other bugs fixed!