Integration with deepcell

[jacob-rosenthal]

We should have a clean and tested integration with deepcell. For example, we could add a Transform which wraps a deepcell application. This would basically generalize our current implementation of the Mesmer model, since there are other applications in the deepcell_toolbox that we might want to use as well. We could thoroughly test this deepcell application transform and be confident that it would work for Mesmer or any of the other applications, plus new ones in the future as long as they stick to their API

Current blocker: specifying the environment in environment.yml and setup.py which has pathml and deepcell. I removed deepcell dependency to fix #195 but it may be worth giving it another shot at getting it to work