Complete the GUI for the current functions in WFEngine class

Features:

1. Provide a selector for the wfengine.json file (similar to launchpad) in the "Manage engine" section
2. Move the query and the firework_id widgets to the relevant sections.
3. A button for cancelling node reservation and execution
4. A button for adding a new node in the Manage nodes section. A little bit complicated interface - a Python function from the notebook should be used.
5. A button to update and update-rerun a node in the Manage nodes section.
6. Adding a workflow from the database using a fw_id, not only by selecting a YAML/JSON file.
7. Adding a workflow from a Python object in the notebook, not only by selecting a YAML/JSON file.
8. Add dynamic configuration of the Python path using a button. Probably another new package, definitely a another module.

Update the relevant docs after adding the features.