There are 2 kinds of ".Editorconfig" in code, one is `JSON string` for
the web edtior, another is `*editorconfig.Editorconfig` for the file
rendering (used by `TabSizeClass`)
This PR distinguish them with different names.
And by the way, change the default tab size from 8 to 4, I think few
people would like to use 8-size tabs nowadays.