AWS: add handlers for Datasets
AWS: fix Manager and Testcase handlers
AWS: update to use SubmissionResults
AWS: allow to see submissions on a certain dataset
AWS: move remaning task fields in datasets
AWS: fix (3)
AWS: fix (6)
AWS: Add useful links for navigating between submissions and tasks.
AWS: Add support for dataset previewing and notifying students of changes.
AWS: notify other services when Datasets or Testcases change

In particular, notify them when a Dataset is created, updated or deleted
and when Testcases are added or removed, since this could cause a change
in the ScoreTypes used by ScoringService (either in their name, their
parameters or the public testcases).

Also, when the set of the to-autojudge Datasets of a Task changes (when
a new Dataset is activated or when the autojudge flag is toggled),
notify both EvaluationService and ScoringService so they can check if
they find new submissions or user_tests that need to be processed.
TV: Send correct datasets to RWS.

 - We only send results for the active dataset to RWS.
 - We also now re-send all results for a task when the dataset is changed.
Fail-proof against broken scorers and setups
AWS: Optimize DB query for submission information.

Avoid n queries per submission to fetch submission result, token, files, etc,
by preloading them in the same query. Load time for a page with 1000
submissions goes from 30 seconds to about 1 second. Similar results with ES and
SS when they go to check on ALL THE SUBMISSIONS.
AWS: Improve performance of rankings page.
cmstestsuite: update to manage Datasets

We don't actually test datasets, but just put everything into the default
dataset.
SpoolExporter: update to manage Datasets
YamlLoader: update to manage Datasets
YamlReimporter: update to manage Datasets
ContestExporter/Importer: change the --light behavior

And benefit from SubmissionResults and UserTestResults.
Adapted Test.py to isolate & task versions