CHANGE-709 - Refactor logging infrastructure (continuation)

CHANGE-709 - Refactor logging infrastructure (continuation from earlier changes)
- fix chicken/egg problem with log initialization
- add explicit logging messages in more places
- relocate log-delete code to logwriter
<a href='#crh-start'></a><a href='#crh-data-
> `zco_` prefix vs local variable

I went back and looked deeper into your suggestion ... and realized that I was replying based on thinking I was still globaling $zco_notifier (which is a requirement in the rest of procedural core code) ... but that's no longer necessary because of the injection, so you're right, the zco_ prefix is not needed.

> There's a shorthand for this: `$this->notifier = $zco_notifier ?: new notifier;`

If $zco_notifier (or $aNotifer, whatever), is null, then a PHP Warning is triggered.  And implementing an isset() makes the shorthand unusable.