Source environment before running any command

Created by: jhchabran

Makes the programming languages section auto fixing.

• I had to move the asdf installation step to the programming languages section, otherwise that section could be entered without being fixable.
  • While not perfect, because running any other step than asdf will always fail, autofixing it will pick them in order and will work.
  • asdf is an autofixing dependency and won't be installed if the language checks passes. It will if the user asks to autofix things.
• Handles the cases where asdf is installed but the language isn't. breaks the independence from asdf promise, removed.
  • asdf shim will be picked up, which incorrectly asserts that the language is present.
  • It will check compliance with .nvmrc though we can remove that in another PR.
• All commands being run are run in a fresh shell, which eliminates the need to restart sg.
• Adds a message explaining to the user how to exit. A handler is set to print a warning about reloading the environment to get everything to work if they do.
  • Because we're sourcing the env before every step, it would be confusing to have the checks passing but not outside sg setup.
• It picks the right shell configuration file based on the current shell.