add nonstop, uc and ucf to build, plus scripts include-recipes.sh and show-package.sh

This depends on cookbook!332 (merged)

Add make commands uc.recipe and ucf.recipe for convenience.

• uc removes the recipe source and target
• ucf removes source and target and does a fresh fetch of source

Add REPO_NONSTOP?=--nonstop as a config option to allow repo.sh to continue on error, which will prevent a single recipe failure from stopping the build. Note that an error for a single recipe causes undefined behavior, including no package, an empty or bad package, make image failure or an image with bad contents.

Add script include-recipes.sh that generates a toml snippet for the filesystem config, including all recipes that match a given string.

scripts/include-recipes.sh "TODO.*text"

It will generate recipe_name = {} for each matching recipe with the TODO as a comment to quickly keep track of the recipe status while testing inside of Redox.

Add script show-packages.sh, which will list the contents of the stage and sysroot directories for a given list of recipes.