Fix EZP-21055: creating content using API causes memory leaks

This has been reported by @gggeek / KeyTech, and as the issue spans across eZ Publish, StashBundle and Stash there are 3 parts:
- This PR
- https://github.com/tedivm/TedivmStashBundle/pull/23
- https://github.com/tedivm/Stash/issues/79

This PR handles the eZ Publish issues in the following way:
- Change unCachedHandler logging data structure to be more efficient
- Set a configurable $maxLogCalls to limit number of uncached SPI calls
- Change how Search calls are logged to not keep the argument objects in memory, just log class name

An optional follow up would be to configure prod to set $maxLogCalls to 0, but by default these measures should stop the memory use to increase forever already.