Draft: lowercase use_link option for arrays

Inside the class `_DraftLink` the `onDocumentRestored` function
tests for the existence of the old attribute `useLink`. If it is
present, it uses it to define the new variable name `use_link`.
This is done use Python naming conventions.
The old `useLink` is deleted so it is not longer saved
together with the object when the document is saved.

src/Mod/Draft/draftobjects/circulararray.py

@@ -41,5 +41,5 @@ def make_circular_array(obj,
     obj = Draft.makeArray(obj,
                           arg1=r_distance, arg2=tan_distance,
                           arg3=axis, arg4=center, arg5=number, arg6=symmetry,
-                          useLink=use_link)
+                          use_link=use_link)
     return obj