Added separate files for ATN

[tdulcet]

• Added separate summary and description files for ATN.
  • They are the same as the AMO files, just without most of the emojis (due to Unable to add most emojis and many other Unicode characters to add-on summary and description thunderbird/addons-server#170). I also removed the browser and webpage specific stuff that does not apply to Thunderbird.
• Minor copy edits to English text. (extracted from Added Emoji Autocorrect. #93)

This is part 3 of the changes needed for Thunderbird support.

[tdulcet]

@rugk - Just a friendly ping since it has been almost a year. 🙂 (I do not have permission to request a review.)

[rugk]

Okay, but the descriptions are like 99% the same, are not they? 🙃

I mean it's okay, just to keep that in mind for maintenance reasons.

It's of course fine and thanks for pinging, GitHub inbox is like going crazy…