Regrading Bugfix: Updating stepdata on massive amounts of questions/stepdata records lead to miserable performance

[danowar2k]

Going from a Postgres server here:

• Nr. of matrix questions: ~56.000
• Nr. of matrix stepdata records. ~20.000.000

This led to run times of 3+ hours for the update. Combined with local storage problems this led us to abort an attempt to switch to this version.

I've already analyzed memory usage and performance for queries etc. and will provide a PR with a fix for these atrocious performance issues with my data update for #95.

I've successfully lowered runtime on test servers from 2:30 hours to 10 minutes. Currently testing with remote database server Moodles, but I'm optimistic.

[danowar2k]

PR #150 fixes this.

[danowar2k]

Grrr, why does Github not link this.

#150 fixes this.