postgresql_service_watcher: created a new basic postgresql service watcher

There is a new dependency for postgresql so need to execute `bundle install` in nerve environment, if installation fails install `sudo apt-get install libpq-dev` and then re-install gem

For more details:
[How to use ruby environment for Nerve and Synapse](https://github.com/dubizzle/smartstack-cookbook/wiki/How-to-use-ruby-environment-for-Nerve-and-Synapse)