create a Java GUI with a REPL and canvas window

Create a Java GUI that contains a REPL but can also spawn a turtle graphics canvas.

This issue represents the Java version of the the issue in #11, which targets JavaScript.

There is a library for creating a REPL in a Java Swing GUI: https://github.com/alandipert/clj-swingrepl
And Seesaw makes Swing programming actually fun: https://github.com/daveray/seesaw

Creating a JS-targeted REPL as in #11 obviously has more relevance and reach, but having a Java version is better than not having one, all things being equal. At the time of this writing, neither exists, so deployment of clojure-turtle is still a bit 'manual'.