Slack notification support for command line usage

[ydnath]

@ksator requested this.

We have email notifications. What about adding slack notifications?
For jsnapy with ansible, there is no need to add it as we can use the slack notification ansible module.
For jsnapy with python, there is no need to add it as we can use python libraries for this.
So this is only for jsnapy command line tool and I think this is not difficult as there are python modules for this. It will allow slack notifications from jsnapy in addition to the existing slack integrations with GitHub, Travis, pyez (python), ansible, …

Cheers

Khelil

[eeishaan]

It would be better if one uses third party cli software built for this purpose. One example: https://github.com/candrholdings/slack-cli . This helps to focus on the tools itself. @ydnath shall I close this?