Set storage directory to make subdirectory.

[JoranAngevaare]

We should make the the storage directory make a sub directory.

For example:

# From
016389-raw_records-rfzvpzj4mf/
# To
016/016389-raw_records-rfzvpzj4mf/

If we allow generic characters for the run-numbers, each head e.g. 016 in this case, the main directory will have at most 26^3=17576 directories/datatype/lineage. From ~10000 onward one might expect FS slowness due to this.

We might very well make this an configurable option.