Rationalize apps directories inside the docker container

[nicobo]

E.g. ; files that don't change :

• /etc/nicobot/config.yml
• /etc/nicobot/i18n.en.yml
• ...

And files that are automatically downloaded/(re)generated :

• /var/nicobot/omemo/*
• /var/nicobot/signal-cli/*

[nicobo]

But as of today, nicobot has only one parameter for both (-C), so it's wiser for now to stick with everything in /usr/src/app/* :

• /usr/src/app/config.yml
• /usr/src/app/.omemo
• /root/.local/share/signal-cli -> /usr/src/app/.signal-cli

For the sake of simplicity (and shorter docker command lines), this could event be changed to something like /nicobot or /app.

[nicobo]

Done :

• /etc/nicobot/ for default configuration files
• /var/nicobot/ for custom & temporary files
• In docker, -c /run/secrets/config.yml is used to map a secret config.ym