Allow user update slice title in visualize flow (#3466)

* 1. after user make sql query and visualize, allow user click title to update slice title, and create a new slice at the same time.
2. don't save new title if it is empty. Will still show old title.

* change saveSlice call response and update explore view

superset/assets/spec/javascripts/profile/EditableTitle_spec.jsx

@@ -81,5 +81,12 @@ describe('EditableTitle', () => {
       // no change
       expect(callback.callCount).to.equal(0);
     });
+    it('should not save empty title', () => {
+      editableWrapper.setState({ title: '' });
+      editableWrapper.find('input').simulate('blur');
+      expect(editableWrapper.find('input').props().type).to.equal('button');
+      expect(editableWrapper.find('input').props().value).to.equal('my title');
+      expect(callback.callCount).to.equal(0);
+    });
   });
 });