config: Mod() should return config dict

this helps for coded configuration

Change-Id: I07bdf72f77082f31ee86192faec63df706dcbf56
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/35803
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Georg Brandl <g.brandl@fz-juelich.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

frappy/config.py

@@ -95,7 +95,9 @@ class Collector:
         self.cls = cls
 
     def add(self, *args, **kwds):
-        self.list.append(self.cls(*args, **kwds))
+        result = self.cls(*args, **kwds)
+        self.list.append(result)
+        return result
 
     def append(self, mod):
         self.list.append(mod)