Updated to new breaking changes in discord.py 2.0a

The discord.py author announced to work again on it's library along with some breaking changes which I needed to take care of
in particular:

• 28f8c44 is now freezed on a particular discord.py commit
• b034eff cogs are now mostly asynchronous, more info can be found here
• 8f27413 messages_content intent is now needed to read messages content and actually read commands
• 3fd4422 the guild object doesn't have a region anymore

Big Python and Discord.py update

This release marks two big new milestones:

• 5a477d4 updated to Python 3.9 with distroless Debian 11 image in the Docker build
• a2370ba updated to the (most likely) last ever Discord.py version 2.0 Alpha

Unfortunately the founder of Discord.py decided to step down as maintainer and the Discord.py repository is now in read-only mode, read further about this here: https://gist.github.com/Rapptz/4a2f62751b9600a31a0d3c78100287f1
given that I share a lot of the complaints against Discord I'm unsure about the future of this Discord bot in the long term

August 2021 maintenance

• f721bcd fixed a typo which broke the :nsfw command
• 0374e1e renamed the systemd service example to actually make sense

June 2021 maintenance

• f65dcd4 changed the way how the bot detects it is run via docker
• 5f18e02 bumped websockets to version 9.1
• 36d4f66 bumped discord.py to version 1.7.2

April 2021 maintenance

• replaced client.logout() with client.close() since it is now declared deprecated since discord.py 1.7
• updated to discord.py 1.7
• DISCORD_SELFASSIGNROLE and selfassignrole works again

Refactored main.py

The bot is now properly inside it's own ShinobuBot class. This should help in the future for utilizing dpytest to finally have something like unittests for the bot.

Removed :tags command

Since using now mainly docker I'm to lazy to make the reaction sqlite database used in the :tags command work in a stateless container

Timezone is now configurable

Set it either in the config.py via

__timezone__ = 'Europe/Berlin'

or via environment variables for Docker/Heroku:

DISCORD_TIMEZONE: 'Europe/Berlin'

Finally Docker support

Shinobu-chan now works inside Docker! I provided Dockerfile and an example for a docker-compose.yml
f191c1e added a check for the :status command if the bot is inside a docker container or not