Move from the Application Dependency management tutorial to a guide page instead

[pradyunsg]

See #912 for full context.

The idea is to present the available dependency management tooling options as a gradient of increasing complexity + scope-of-tooling -- as done in Installing Scientific Packages -- putting things like manually managed pip requirements.txt files, pip-tools, pipenv and poetry on "equal" footing; moving away from a guided tutorial to using pipenv to being a guide on how to pick the right option for you.