Refactor summary data

[LDSamson]

Closes #263. See also #223 (comment).

This should make the app faster at start up but also after saving a review.

[LDSamson]

@jthompson-arcus new method is about a factor 3 faster when I do a quick benchmark on a big dataset (using the code below and setting duplications to 100, and then using a microbenchmark to compare both versions): #223 (comment).

Biggest change comes from the change of summarize_review_data().
Removing temp_table creation in the SQL code and removing the indexing does not change much in speed so we could remove that to reduce complexity. Or remove the SQL query if you think it is not worth to change to this pattern.