Add StoredObjectVersionApiController and corresponding test

Added a new class StoredObjectVersionApiController in ChillDocGeneratorBundle which lists versions of a specified stored object. Corresponding unit test has been added as well. Made modifications in `StoredObject.php` to make the versions selectable. Also updated the API specifications to include a new GET route for retrieving versions.

src/Bundle/ChillDocStoreBundle/chill.api.specs.yaml

@@ -105,3 +105,28 @@ paths:
                 404:
                     description: "Not found"
 
+    /1.0/doc-store/stored-object/{uuid}/versions:
+        get:
+            tags:
+                - storedobject
+            summary: Get a signed route to post stored object
+            parameters:
+                - in: path
+                  name: uuid
+                  required: true
+                  allowEmptyValue: false
+                  description: The UUID of the storedObjeect
+                  schema:
+                      type: string
+                      format: uuid
+            responses:
+                200:
+                    description: "OK"
+                    content:
+                        application/json:
+                            schema:
+                                type: object
+                403:
+                    description: "Unauthorized"
+                404:
+                    description: "Not found"