This moves the remaining DTML queries to Python, dropping the 'activity' skin.

Dealing with conflicts of uids is easier if the inserted uids are consecutive:
now, only 1 random value is generated, as base uid. This also preserves the
order of insertion, which is wanted for performance reasons:
- No more random write in the primary index.
- When modifying several lines of several documents, 1 document being processed
  at a time, we'd like that any grouped activity (usually indexation) follows
  the same order, so that a processing node prefer many lines from a few
  documents instead of mixing lines from too many documents at the same time.
  This is usually better for caches.