Mobile-env

Fixes in the CI and doc build system. `mobile-env` functionality itself unchanged.

First major release of `mobile-env`:

* Simple, lightweight simulation environment for reinforcement learning in wireless mobile networks
* Easy installation and configuration
* Many options for extension, e.g., user movement, quality of experience models, channel models, etc.
* [New interactive Google CoLab demonstrating some of these features](https://colab.research.google.com/github/stefanbschneider/mobile-env/blob/master/examples/demo.ipynb)

* Added tutorial notebook
* Removed poetry in favor of plain pip
* Multiple, small adjustments and refactoring without added functionality

Core Environment:
- added rendering functionality
- ensured customizability of core simulation components
- added various simulation scenarios (small - large)
- added handlers for centralized & multi-agent setting
- added environment wrapper for integration with RLlib for multi-agent setting

Builds:
- added CI/CD and documentation
- updated pypi-publish workflow
- support for python3.7 & python3.8