Add .editorconfig (see editorconfig.org) (#2943)
Add .editorconfig (see editorconfig.org) (#2943)

This file uses the same settings which we currently have in our vim modeline,
but can be picked up by many different editors without having to add and
maintain editor-specific modelines in all of our source files.
Airblader/i3-original,i3/i3,i3/i3,Airblader/i3,cornerman/i3,i3/i3,Airblader/i3,Airblader/i3-original,Airblader/i3-original,stapelberg/i3,cornerman/i3,stapelberg/i3,stapelberg/i3,cornerman/i3,Airblader/i3-original,Airblader/i3-original,stapelberg/i3,cornerman/i3,i3/i3,Airblader/i3,Airblader/i3