Extract io layer to writer/reader class

Created by: stefanoborini

Extracted IO layer into writer and reader classes, and create model objects with support from the bundles.

force_bdss/io/workflow_writer.py

+import json
+from traits.api import HasStrictTraits
+
+
+class WorkflowWriter(HasStrictTraits):
+    """A Writer for writing the Workflow onto disk.
+    """
+    def write(self, workflow, f):
+        """Writes the workflow model object to a file f in JSON format.
+
+        Parameters
+        ----------
+        workflow: Workflow
+            The Workflow instance to write to file
+
+        f: File
+            A file object on which to write the workflow, properly serialized
+            into JSON.
+        """
+        data = {
+            "version": "1",
+            "workflow": {}
+        }
+
+        wf_data = data["workflow"]
+        wf_data["multi_criteria_optimizer"] = {
+            "id": workflow.multi_criteria_optimizer.bundle.id,
+            "model_data": workflow.multi_criteria_optimizer.__getstate__()
+        }
+        kpic_data = []
+        for kpic in workflow.kpi_calculators:
+            kpic_data.append({
+                "id": kpic.bundle.id,
+                "model_data": kpic.__getstate__()}
+            )
+
+        wf_data["kpi_calculators"] = kpic_data
+
+        ds_data = []
+        for ds in workflow.data_sources:
+            ds_data.append({
+                "id": ds.bundle.id,
+                "model_data": ds.__getstate__()
+            })
+
+        wf_data["data_sources"] = ds_data
+
+        json.dump(data, f)