Find some way to detect performance regressions

[acelaya]

Recently there was a change in a query that made its performance drop drastically, resulting in a nasty bug.

The problem is that it was not detected, because all tests kept passing, and it was not obvious when using small amounts of data.

Using something like https://github.com/phpbench/phpbench it should be possible to benchmark certain aspects of the app (primarily database queries. They are usually the bottlenecks), and fail continuous integration if performance had been deeply affected by some change.