WIP: Add Python 3 support

I'm in the process of upgrading the source code to support Python 3. As of this PR all pure Python is ported, but running into some Cython/Java compilation issues:

```
copying javabridge/jars/rhino-1.7R4.jar -> build/lib.macosx-10.5-x86_64-3.4/javabridge/jars
running build_ext
running build_java
javac java/org/cellprofiler/runnablequeue/RunnableQueue.java
jar cf javabridge/jars/runnablequeue.jar -C java org/cellprofiler/runnablequeue/RunnableQueue$1.class -C java org/cellprofiler/runnablequeue/RunnableQueue.class
javac java/org/cellprofiler/javabridge/test/RealRect.java
jar cf javabridge/jars/test.jar -C java org/cellprofiler/javabridge/test/RealRect.class
cython _javabridge.pyx _javabridge_mac.pyx _javabridge_nomac.pyx

Error compiling Cython file:
------------------------------------------------------------
...
                bresult = jnienv[0].CallByteMethodA(jnienv, this, m_id, values)
            result = bresult
        elif sig == 'C':
            with nogil:
                cresult = jnienv[0].CallCharMethodA(jnienv, this, m_id, values)
            result = unichr(cresult)
                          ^
------------------------------------------------------------

_javabridge.pyx:831:27: undeclared name not builtin: unichr
```