Rabbit VCS on Ubuntu 18.04 - not showing menu in Nautilus

You can make RabitVCS working again on Ubuntu 18.04 LTS by copying its python extension to special directory inside your home folder:

sudo apt-get install rabbitvcs-nautilus

mkdir -p ~/.local/share/nautilus-python/extensions

cp /usr/share/nautilus-python/extensions/RabbitVCS.py \
~/.local/share/nautilus-python/extensions

Then restart Nautilus (Files) with

nautilus -q

and enjoy:

I hope it is fully-functional.

Notes:
1. if you need only Mercurial you can use tortoisehg-nautilus package.
2. if you see two RabbitVCS menu sections then remove python extension from home folder with rm ~/.local/share/nautilus-python/extensions/RabbitVCS.py.