Add .editorconfig

[ehmicky]

This adds an .editorconfig file.

[erezrokah]

I think we can set options.editorconfig to true in .prettierrc.json and remove the printWidth setting from it, WDYT?
See https://prettier.io/docs/en/api.html#prettierresolveconfigfilepath--options

[ehmicky]

Good point! I have just removed the redundant Prettier option printWidth.
The editorconfig option in Prettier is true by default, so we don't need to explicitly enable it (I have just tried it locally to make sure).