Add EditorConfig setting

Allows for consistent spacing and indenting when combined with supported
IDEs

.editorconfig

@@ -0,0 +1,9 @@
+# editorconfig.org
+root = true
+
+[*.js]
+indent_style = space
+indent_size = 4
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true