fixing "params" handling in section entries

"params" is interpreted differently in section vs workload entires in
the agenda; previously, this was handled in the generic entry
construciton function by examining the ID prefix of the entry to
distinguish between the two.

This is unreliable as the user may specify their own IDs that won't have
the expected prefixes. To handle this, the "params" alias resolution for
sections is now handled in section specific part of entry processing
(workloads are handled autmatically because that is the default for
the corresponding JobConfig config point).

wa/utils/serializer.py

@@ -126,6 +126,10 @@ class json(object):
     def dump(o, wfh, indent=4, *args, **kwargs):
         return _json.dump(o, wfh, cls=WAJSONEncoder, indent=indent, *args, **kwargs)
 
+    @staticmethod
+    def dumps(o, indent=4, *args, **kwargs):
+        return _json.dumps(o, cls=WAJSONEncoder, indent=indent, *args, **kwargs)
+
     @staticmethod
     def load(fh, *args, **kwargs):
         try: