Preliminary Python3 support

Hi Deniz,

This is the first batch of commits to make allow concoord to run on Python3.
Most of my tests are on python3, but I did perform some sanity checks on Python2.

Please not that before installing the different versions you have to clean the build directory (as the built .py files are very different).  I use the following command:  "sudo git clean -fdx"

My next work is going to be on allowing methods to include non-hashable python objects (such as a dict, etc). This will change both the proxy object and the method invocation code.

Let me know if you want to to make any further changes to these commits.

Thanks,
Liran