New module for Heka

I couldn't find a public module for heka so I've created this based on the proof of concept I did.

It's pretty unopinionated and configurable, so could probably be later moved to gds-operations and released on the Forge. I suspect that some more opinionated plugins like nginx and rsyslog will live in our internal repo.

The diff is against what gds-operations/puppet-module-skeleton creates.