Add i18n and custom responses

[doZennn]

Adds localization support and the ability to customize the bot responses as a side effect.

I manually combed through, and organized every string into their own .yml file. There are only some minor changes to menu buttons such as "Back" and "Cancel". I also Changed "Overseerr" to "Seerr" while I was at it.

Adding new languages

Make a copy of the English files in i18n/ and change the filename to the language you want to translate to.
e.g. messages.en.yml -> messages.de.yml. You also need to change the root key in the .yml en: -> de:

If a string is missing or not translated, it'll fall back to the English file, if for some reason the English file also doesn't have a definition it'll show up as the key name. e.g.check.usage instead of Usage: /check <title>

Custom responses

Users can also change what the bot responds with if you copy the .yml you want to change and put it in data/i18n/, the bot will load those over the defaults. If the bot updates and the user has an old yml, it'll just fall back nicely as explained above.

I use this cause I don't like how some of the responses are worded.
This serves as a potential fix for #34 by just changing these: i18n/check.en.yml