[style](editorconfig): Commit initial EditorConfig config for code style

Soon to be added: wiki page about expected code style for Barrier.
Also, docs when that's ready.

Signed-off-by: Dom Rodriguez <shymega@shymega.org.uk>

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+indent_style = space
+indent_size = 4