Surveillance-bot

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* Uses public docker image in docker compose file.
* Adopts semantic versioning.

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* Improves code style.
* Forces virtualenv upgrading in travis environment.
* Bumps python-telegram-bot and opencv-python versions.
* Fixes breaking changes with python-telegram-bot.
* Speeds up docker image creation.
* Adds python 3.9 support.
* Uses opencv-python-headless package.

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* Initial release.