I tried installing the Toolset but it didn't seem to recognize the file.
I downloaded the toolset.zip file off of the website you had provided (even downloaded both to test it).
I then tried to install it via the 'Install Extension...' button inside of Stencyl, but it did not seem to do anything when I tried to install it.
So I tried the other way and pasted the Toolset folder into the Stencyl_Extensions folder, but still no luck.
When downloading the toolset Extension Manager zip folder, there appeared to be another Zip folder within that, plus the java file. I extracted that one as well and there appeared to be yet another folder with the Java Executable within that.
I tried installing all alternative options, but still no luck.
Here are screenshots of my extensions, and the file that I had downloaded within the Extension Directory.