Add environment setup into stim

[lwahlmeier]

It would be nice to have stim be able to automatically setup/download common utilities for different environments.

Since not all environments are the same it would be nice to have the following features:

• Ability to statically set versions of utilities for an environment/cluster
• Ability to auto-detect versions of utilities for an environment/cluster
• Ability to download needed versions of utilities for the environment/cluster
• Ability to launch a shell with all the needed utilities and versions configured for the environment/cluster