Add scriptFile parameter to allow users to specify the script that gets embedded

Currently, the plugin has a fairly basic script that it injects which doesn't allow for things like overriding jvm parameters from the command-line.  It would be nice to have the ability to override such things, but it's not safe to assume that everyone will want it done the same way.

Instead of picking how it should be done, giving users the ability to specify the script that they want embedded seemed like the safest solution with minimal impact.