[NFY] Feature/browse cookbooks

- lists all cookbooks,
- shows cookbook details: description, maintainer, platforms, dependencies, providing, conflicting, ...
- lists all files in a given cookbook,
- shows a cookbook's readme (using `cookbook.metadata.long_description`),
- shows raw json metadata,
- lists all recipes w/ descriptions (if such exist),
- shows recipe code,
- shows the contents of every file, with highlighted syntax where possible.

The data is presented in a very basic way and could definitely use some reorganization; pointers are very much welcome!