Restore compile and run functionality

[hinerm]

@ctrueden and I have been discussing this in the context of the current deployment goals.

With the changes to file structure and second look at making install work in the script editor, I think it would be nice to get a minimal version of Compile and Run working again.

My proposal is to use a dedicated class loader that is re-created during each execution, and only support one-off plugins.

[ctrueden]

Yeah, I think it should just call the same functionality that the Script Editor uses when running Java code.