Implement a REPL

[wolfv]

When a recipe fails, it's a pretty difficult and annoying process to change the recipe, add patches, ...

We want to make this as smooth as possible. The goal is to implement a REPL when recipes fail, using prompt_toolkit:

• open editor in workdir, modify the contents of workdir to interactively create patch files and add them to the recipe
• change dependencies in the recipe.yaml file and the host / build environment are immediately updated & changed
• change the build script in the recipe dir and re-run the recipe script
• clean workdir / host easily to re-run recipe quickly
• use ccache if possible?