General Refactor + Interactive Recipe Editor

[4jamesccraven]

Interactive recipe editing + several enhancements and refactors to recipe logic.

Recipe Editor

• Change the name, description, and contents of a recipe interactively with mk edit
• Get LSP support for the contents of a recipe's files by invoking $EDITOR while editing them.

General Refactor

• Recipes are now made "canonical" before saving. This entails copying the recipe to a temporary directory and creating a new representation based on that directory (using the typical imprint machinery).
• Common logic such as instantiating recipe(s), verifying their existence, and getting their location on disk have been extracted into standalone functions to unify behaviour.
• Functionality has been added to detect if a recipe is externally managed (i.e., is a symlink from something like home-manager or gnu stow).