Add script to run TheengsGateway on Linux

[koenvervloesem]

Description:

This makes it possible to run Theengs Gateway simply as TheengsGateway instead of python -m TheengsGateway on Linux.

Rationale: I'm working on a snap to package Theengs Gateway on Linux (Ubuntu, more specifically), and this needs to be able to run the Python module as a script in bin/ (or at least I haven't found a way to do it otherwise).

By the way, if you're interested in hosting the snap, I'm willing to publish and develop it under the theengs organization on GitHub if you create a repository gateway-snap.

Checklist:

• The pull request is done against the latest development branch
• Only one feature/fix was added per PR and the code change compiles without warnings
• I accept the DCO.

[1technophile]

Thanks, I added the repo and invited you