Allow deepcell_imaging module to run in "development mode" in the venv

[dchaley]

I forget what it's called when a module installs a symlink to its live content into the venv using pip. But whatever that is, we need to do it, so that we can access our code without hacky direct file imports.

[dchaley]

We solved this by running this in the venv:

pip install --editable .