Switch to Maven to build the Java bits.

Maven is now used to update the constants, build the Java code, call make to
build the native library, and run all the tests. I have removed the "install"
and "uninstall" targets; instead, the expectation will be that the JNI library
will be placed somewhere on java.library.path and the JAR file will be used as
usual (e.g. in a downstream Maven project, or placed on the classpath of your
project).

Since Maven is now running our tests, this eliminates the need to bundle test
dependencies in `testdep`, and makes the project structured more like a typical
Java project.

.gitignore

@@ -45,7 +45,6 @@ _*.txt
 _*.diff
 tmp/
 
-bindings/java/unicorn_Unicorn.h
 bindings/python/build/
 bindings/python/dist/
 bindings/python/src/