648 ensure consistency of count columns

Shall fix #648.

After deploying this to a machine, we should check that there are actually no mismatches anymore.
This query will return the count of ontologies with mismatches:

```SQL
SELECT COUNT(compared.id) FROM
(
  SELECT DISTINCT ON (id) * FROM (
    SELECT o.id, o.name, o.entities_count, COUNT(e.id) as counted_entities FROM ontologies o
      INNER JOIN entities e ON e.ontology_id = o.id
        GROUP BY o.id ORDER BY o.id
    ) e
    JOIN (
      SELECT o.name, o.sentences_count, COUNT(s.id) as counted_sentences FROM ontologies o
        INNER JOIN sentences s ON s.ontology_id = o.id
          GROUP BY o.id ORDER BY o.id
      ) s USING (name)
    JOIN (
      SELECT o.name, o.versions_count, COALESCE(COUNT(v.id), 0) as counted_versions FROM ontologies o
        INNER JOIN ontology_versions v ON v.ontology_id = o.id
          GROUP BY o.id ORDER BY o.id
      ) v USING (name)
    JOIN (
      SELECT o.name, o.metadata_count, COALESCE(COUNT(m.id), 0) as counted_metadata FROM ontologies o
        LEFT JOIN metadata m ON m.metadatable_id = o.id AND m.metadatable_type = 'Ontology'
          WHERE o.type = 'SingleOntology'
          GROUP BY o.id ORDER BY o.id
      ) m USING (name)
    JOIN (
      SELECT o.name, o.comments_count, COALESCE(COUNT(c.id), 0) as counted_comments FROM ontologies o
        LEFT JOIN comments c ON c.commentable_id = o.id AND c.commentable_type = 'Ontology'
          WHERE o.type = 'SingleOntology'
          GROUP BY o.id ORDER BY o.id
      ) c USING (name)
) compared
WHERE compared.entities_count != compared.counted_entities OR
      compared.sentences_count != compared.counted_sentences OR
      compared.versions_count != compared.counted_versions OR
      compared.metadata_count != compared.counted_metadata OR
      compared.comments_count != compared.counted_comments;

```

But i suggest to run this query on *ontohub.org* and *staging.ontohub.org* **only**.
That is because *develop.ontohub.org* has more than 12.000 ontologies, which will put
a strain on the machine. When i executed it ran out of temporary-file-memory.
But it'll work on *ontohub.org* and *staging.ontohub.org*.
Yes, see the last commit in this pull-request (04b23def01226b4ed4fb11763c079648df702d2f).