[plotters][serializers] Add explicit data json field

This allows the PlotterParameterCreationSerializer to properly
handle the json given as data parameter.

beat/web/plotters/serializers.py

@@ -112,6 +112,7 @@ class PlotterParameterCreationFailedException(Exception):
     pass
 
 class PlotterParameterCreationSerializer(ContributionCreationSerializer):
+    data = serializers.JSONField(required=False)
 
     class Meta(ContributionCreationSerializer.Meta):
         model = PlotterParameter
@@ -223,7 +224,6 @@ class FullPlotterParameterSerializer(PlotterParameterAllSerializer):
 
     def get_plotters(self, obj):
         all_plotters = Plotter.objects.all()
-        serializer = FullPlotterSerializer
         results = {}
         for plotter in all_plotters.iterator():
             serializer = FullPlotterSerializer(plotter, context=self.context, fields=['id', 'accessibility', 'modifiable', 'deletable', 'is_owner', 'name', 'fork_of', 'last_version', 'previous_version', 'short_description', 'description', 'version', 'creation_date', 'data', 'sample_data', 'declaration'])