Add editor config so trailing whitespace is removed automatically

Author: matthewpwilson

.editorconfig

@@ -0,0 +1,8 @@
+# top-most EditorConfig file
+root = true
+
+[*.{js,ts}]
+indent_style = space
+indent_size = 4
+insert_final_newline = true
+trim_trailing_whitespace = true