Add set category for a Data Stream. A data Stream can belong to many Data Sets (or any other 'collections' or 'sets').

During ingestion the relation between Data Set and Data Stream is set on Data Ingestion Line. This seemed enough for small Data Sets (few thousands of Data Streams). With large Data Sets this is inefficient as getting list of Data Streams for a Data Set takes sometimes tens of minutes.
Thus we needed a faster way to loop up: which is an explicitl relation over set category and proper MySQL indexing.
This commit is a trade-off between cost of storage (i.e. a category) compared to scalability and performance of a system.

This reverts commit 793fe76f.

Add an utility script to check md5sum of all Data Streams for a Data Set (uploaded from file system) and what we have in reallity.

Rather than read Data Streams' properties from ZODB object do read them from ZSQL's brain object - much faster when data sets contain hunreds of thousands of files.

Index directly the relation between a Data Stream and its logical set (in this case of default Wendelin model - Data Set).

See merge request nexedi/wendelin!73

See merge request nexedi/wendelin!72

See merge request nexedi/wendelin!71

See merge request nexedi/wendelin!70

See merge request !69

See merge request !68

See merge request nexedi/wendelin!67

- show also validated data streams

See merge request !66

See merge request !65