nemo-rabbitvcs

This pull brings in a fully functional and packaged port of the rabbitvcs-nautilus3 extension for Nemo, now named nemo-rabbitvcs (in order to keep with the scheme we have going in this repository).

It works with rabbitvcs-core as found in the Ubuntu and Mint repositories. I've tested the file-manager functions and the package installation.

![Screenshot](http://i.imgur.com/mL3jC.png)

As I've been doing elsewhere, I've added a bit of detail to the usual GNU files (authors etc.).