make Clojure player more idiomatic

I was delighted to see support for Clojure players in GGP; however,
the code really is not very idiomatic.  I've tried to improe it by:

correcting formatting (closing parenthesis never go on a line by themseleves, for example)
using imports to reference Java classes
using the prefered Java interop notation
using a let binding to make the Java interaction clearer