Make the heatmap package releaseable to ros.org buildfarm

[130s]

1st, thanks for a nice package!

I saw this package used to be released into ROS buildfarm (e.g. ros/rosdistro#9324) and met an issue there (e.g. #1). But along with this PR, I ran some CI jobs incl. ROS prerelease test (on Kinetic) on my fork and they are all green for ROS Jade, Kinetic, Lunar.

So, why don't we?

If you need a help for making a release I'm happy to help.

[130s]

Also suggested in this is to activate CI (Continuous Integration) to catch any unknown issues earlier.

ROS offers a few different ways to simplify setting up CI. In this PR, I'm suggesting industrial_ci (admittedly I'm one of the authors&maintainers). It's a set of scripts for CI on ROS. The simple config file in this PR enables CI to run on Travis CI for this repo, including ROS pre-release test that is recommended for packages released on ROS buildfarm.
Contrary to its name, it works for any ROS packages as well, not limited to "industrial" pkgs.

If this looks good, can any admin enable Travis for this repo at https://travis-ci.org/profile/eybee?

---

It's totally up to the maintainers to use which CI tool, how to configure the detail, how to utilize the CI result etc. Just fyi that we as in industrial_ci maintainers have been very active in responding to questions and enhancement requests over a few years.

[130s]

P.S. According to the CI jobs on my fork, the package can also be released into even ROS Indigo, which is still supported until 2019 and is the one that majority of people are still using.