Open python files

[mayansalama]

When hitting the open button, you can also open python files. Fixed some bugs as well

[mayansalama]

@TomKlimovski can open dags and convert them into wmls now. There's a couple of changes I've left out, because I want to consolidate your navbar changes first. Namely:

1. Change icon for convert to python DAG to the python icon
2. Add a navbar button with the current convert to python dag to sort nodes
3. Add a nanbar button to snap to the top left of the dag
4. Add a navbar button to delete the currently selected node

Note that upgrading react-flow-chart to 0.0.14 seems to have fixed a bunch of bugs around dragging and dropping and the zoom functionality