Danger check for "unpackaged" code

[alexevanczuk]

To package all of our files, Gusto has created a pack (see stimpack) called packs/unpackaged_code_that_needs_to_be_organized. All code that we couldn't find a home for we put there, with the intent that users would gradually move it into other packs.

Gusto has an internal danger plugin to aid us with this process. When a new file is created in that pack, we ask them to not create new files that are not packaged. When a file is modified, we ask if they have additional context that could permit them to move the file to a more appropriate pack.

If there is interest, we could port this over to danger-packwerk (with a configurable name for the unpackaged pack).

[schoblaska]

This seems like potentially a good idea! Leaving this issue open for now to track, though it is probably low priority for us.