Integrates the plugin script compilation task with Gradle so we no
longer need to start a new instance of the JVM for each set of plugin
scripts that we want to compile.
Adds separate build tasks for each plugin by auto-discovering plugin meta
files in the build script. Each plugin will automatically have its
main sources and tests compiled, and then it's output added to the game
modules classpath.
This enables support for incremental compilation of scripts, as well as
unit testing using Gradle's test framework.
Gary Tierney