Bt vod synthesize hierarchy

This pull request allows to extract brands from series/episodes rows and creates brand>series>episodes hierarchies based on that. This is because brand entries are not present in the data file.
As I said, episode rows don't have any reference to the parent series' product_id, so the only way for them is to lookup by series title. The alternative is to have 2 different maps: one for checking if a series is already been processed, one for series lookup from an episode row.

Wdyt?