Use sym links for secret doctor modules
Right now we copy the secret doctor modules over into the doctor repo to avoid a
"ModuleNotFoundError: No module named 'util'". That's a bit cumbersome and error prone as there is an additional step after to do after fetching the latest changes to the doctor modules.
We should symlink them as we do with Stem. To avoid the error we could set a proper
PYTHONPATH which our script runs would pick up.