Explicit list of files in modman

Helps with deployment when `auto-append-gitignore` is on for composer projects because dependencies should not be versioned files. Use of `* /` as a modman entry is destructive when updating.

`generate-modman` is a convenience script. It rewrites `modman` file completely. Non-Magento files like `modman` and `composer.json` are excluded. Directories which should not be altered, like `app/code/core` are collapsed to a single entry.