breaking(simon): Replace yokeDart option by roundBack option

This option address fitting for a rounded back.
Something `yokeDart` used to do by adding a dart to the side of the
yoke.

However, in doing so `yokeDart` would change the lenght of the armhole
which is not ideal. The now `roundBack` option instead lengtens the back
in the middle, tapering off towards the sides. Thereby accomplishing
the same alteration without influencing the lenght of the armhole.

config/changelog.yaml

@@ -14,6 +14,7 @@
         See [#642](https://github.com/freesewing/freesewing/issues/642)
       - The `s3collar and `s3armhole` options now allow shifting the shoulder seam
         (`s3` is short for *Shift Shoulder Seam*)
+      - Added the `roundBack` option to replace the `yokeDart` option
     sven: *s3optsAdded
 
   Changed:
@@ -43,6 +44,10 @@
     tutorial:
       - Set department in the config to one of the newly accepted values
 
+  Removed:
+    simon:
+      - The `yokeDart` option is replaced by the `roundBack` option
+
 2.16.2:
   date: 2021-05-05