[meta] Road to 0.1.0 (or 3.0.0)

[GeopJr]

I'm satisfied with the current state of Tooth and ready to make the first release:
(in no particular order)

• Finish branding (New logo #6 Consider renaming? #28)
• Go over all strings, review them and generate pot file (Finalize strings, generate potfile and change app ID #75)
• Update readme
• Take screenshots for the store page
• Website
• Publish to Flathub (Publish to Flathub #15)

About the version: 2.1.0 was the dev version of Tootle that I never changed (I didn't expect it to be packaged prior to an official release), if marking the release as 0.1.0 causes problems in repos, then I guess I'll go with 3.0.0.