Feature: 'explode' a directory

[raboof]

In the following scenario:

- foo (2G)
|- bar (1.5G)
\- baz (0.5G)
- qux  (1.7G)
- quux (0.4G)

diskonaut would show 3 blocks (foo, qux and quux). After entering foo, it would show 2 blocks (bar and baz).

It would be neat to have an option to 'explode' foo in this case, resulting in a view that shows the relative sizes of bar, baz, qux and quux.