periodic database cleaning

[antoinefalisse]

Now that have the celery workers, we could implement periodic cleaning of the database. Example of things to clean:

• If session created more than a week AND no neutral trial => remove
• If session created more than a week AND neutral trial is error => remove
  • TBD since we might want to reprocess, although unlikely
• If trial created more than a day again AND status is recording => remove

The first time we run things, there will be a ton of things to remove, which might bug the workers but that might not be a problem. We could bump resources for like a day or so.

Thoughts @suhlrich and @AlbertoCasasOrtiz? Feel free to add to the list.

[suhlrich]

I like it. Slight update, then let's have Planeks do it!

-If session created more than a week AND no neutral trial => remove
-If trial created more than a day again AND status is recording => remove

[olehkorkh-planeks]

The PR - #144