Improve debian packaging

[pehrsoderman]

Adds a build target to build the debian package with resonable flags, and also adds a test building to the travis ci.

[soufrabi]

This would be really helpful. I believe instructions to build the debian package should also be used in the documentation.

[gollux]

I plan to document Debian packaging before the next release. The current implementation is an experiment I haven't made up my mind yet. Adding a Makefile target to build the package makes sense.

I completely forgot that we have a configuration for Travis CI :) I do not use it and I rather think I should remove it and maybe replace by GitHub Actions.

[pehrsoderman]

The current implementation is an experiment I haven't made up my mind yet.

I just retired our custom packaging of isolate we used internally in Kattis, so I would selfishly appreciate if the debian packaging of isolate remains. Otherwise I have to revert stuff in our infrastructure and resurrect our custom kattis-isolate package :(

I do not use it and I rather think I should remove it and maybe replace by GitHub Actions.

GitHub Actions are very nice. Highly recommended, after struggling with Travis and Drone.

[gollux]

No worries, packaging is here to stay. What I was unsure about were mostly details.

[soufrabi]

I would like to write the github action files for the debian packaging. Isolate does not work well in unprivileged docker containers so testing is not possible. However, build process could be automated.

[pehrsoderman]

Isolate does not work well in unprivileged docker containers so testing is not possible.

If you use a self-hosted runner you can set it up to run Isolate. We do this in our CI. Obviously, you would have to restrict who can run the actions for security reasons.