[RFC] .editorconfig Changes

Opening up a conversation about the .editorconfig defaults.

Points from EC:

* Should .editorconfig encourage the WordPress settings, or encourage the PHP PSR ("proper") settings?
* Whichever one is chosen, when WordPress is downloaded by the generator, the files should be formatted appropriately to avoid any future "giant commit that's all whitespace changes"
* .editorconfig requires plugins to work

Other points

* Currently defaults to 2 spaces for all files requiring each new file to be changed manually.
* Should we even be setting defaults for WP files (including the themes)? Would it be better to limit the .editorconfig to the Genesis core?