chore(*): Added editorconfig

editorconfig configures editors to use the correct indent size and
style.

Replaces #2347
as I recall, we had a conversation on whether shell scripts should be indented with either 2 or 4 spaces but never came up with an answer, which is why some are indented with 2 spaces and some with 4.

@carmstrong @mboersma any opinion against 4 spaces for shell scripts? To me that seems the most reasonable in terms of consistency with the rest of our source code.