Update CreateApp docs

Updates the web CreateApp page to address a couple of small issues:
 - previous instructions specified that the app directory itself was on the ```PYTHONPATH``` whereas it should be the parent directory that is on the ```PYTHONPATH```.
 - import statements in the urls.py example don't work with 5.0 OMERO

To test, follow the CreateApp instructions until you have the "Welcome" message at a new app /index.html.

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