Because the shapekey editor is trying to have a more fancy UI with
sliders on each "Relative" shapekey value, all other animatible
properties were not drawn.

This patch now makes it possible to easily work with actions that have
non "Relative" keys. Before this was almost impossible as the user could
not see what action they had selected or which non relative keys were in
them as the UI would think that the action was empty.

While working on this I also noticed that there are some other
properties in relative mode that is not in the action editor either
(Range Min/Max). I added a TODO about that in the code as one would
probably want to group those together in a nice way with either
respective shapekey.

@@ -1700,0 +1714,4 @@
+      if (!key->adt || !key->adt->action) {
+        return 0;
+      }
+      animrig::Action &action = key->adt->action->wrap();

@@ -1700,0 +1717,4 @@
+      animrig::Action &action = key->adt->action->wrap();
+      FCurve *first_fcu = static_cast<FCurve *>(action.curves.first);
+      for (FCurve *fcu = first_fcu;
+           (fcu = animfilter_fcurve_next(