WIP: Add support for activate/deactivate scripts

This provides a mechanism for packages to run scripts on activate and deactivate.  The idea is that a script would provide a startup and shutdown script that starts something when activated and stops it when deactivating.  The use case I've been working from is supervisord, which would also start other packages that are installed *and* provide a mechanism for inspecting the state of those running applications.

## Tasks
* [x] Modify `activate` / `deactivate` to run scripts
* [ ] Ensure Windows support
* [ ] Modify `conda run` to ensure that anything run in an environment runs activate prior to running and deactivate after it's run
* [ ] Create package that utilizes this feature for testing purposes
* [ ] Create documentation for how to utilize this feature