FEATURE: Provide users the ability to quickly grok the directory structure of a dataset

[sunu]

This topic came up in a discussion with @jlstro.

When trying "go through" a leak or a document dump, users want to quickly figure out which directories are important by looking at their size, the number of files and file types they have and so on.

We can consider showing that information on the collection homepage as a directory tree widget for quick exploration.