SS: remove code leftovers
Remove unused stuff from ScoreType
Remove most internal state from ScoreTypes
Fix SS not sending ranking details to RWSs

Bug introduced in 6e4c42f7dd3135e1464d2c6e9e5db15670d77335 but the
situation wasn't that "safe" even before: we were trying to store a list
of strings in the DB.
Better split duties in SS

Split out all the code that talks to RWS from the one that scores
submissions.
Promote symmetry
Add comments to clarify behavior
RWS: server-side improvements

Catch the case where an update to a submission changes its user or task
and an update to a subchange changes its submission. This also allowed
us to improve the deletion of submissions and subchanges from Scores.
AWS: fix dataset cloning
Add TODO