Refactored the logger to use PSR-3 and Monolog (#6622)

Work in progress for #6622

- master: [![Code Coverage](https://scrutinizer-ci.com/g/piwik/piwik/badges/coverage.png?b=master)](https://scrutinizer-ci.com/g/piwik/piwik/?branch=master) [![Scrutinizer Code Quality](https://scrutinizer-ci.com/g/piwik/piwik/badges/quality-score.png?b=master)](https://scrutinizer-ci.com/g/piwik/piwik/?branch=master)
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`Piwik\Log` and its static methods are still there, but now it is just an empty shell around Monolog. We can also now inject the real logger (Monolog) by using the PSR-3 `LoggerInterface`.

TODO:

- [x] update the [SiteMigration plugin](https://github.com/piwik/plugin-SiteMigration) (https://github.com/PiwikPRO/plugin-SiteMigration/pull/7)
- [x] remove more Piwik code to use Monolog classes (for now I've kept most Piwik code to make sure to keep BC on the behavior, now that it's clearer I can try remove some code)
- [x] simplify the DI config (very complex for now because of BC with INI config)
- [x] write unit tests
- [x] document using `Psr\Log\LoggerInterface` instead of `Piwik\Log`: piwik/developer-documentation#51
- [x] document using PSR-3 placeholders instead of sprintf: piwik/developer-documentation#51
- [x] document how plugins (or users) can override the default config (e.g. have a plugin to use Logstash for example…): piwik/developer-documentation#51
- [x] #6842 separate error handling from logging
- [x] deprecate `Piwik\Log`
- [x] remove `log_only_when_cli` and `log_only_when_debug_parameter`
- [x] `misc/others/geoipUpdateRows.php` can be launched in CLI and should log to CLI output
- [ ] add new config files (in `config/environment/`) to the [debian package](https://github.com/piwik/piwik-package/commit/1424893db56176e97317ff8c55e25fa29ea0c465)
- [ ] merge https://github.com/PiwikPRO/plugin-SiteMigration/pull/7
- [ ] merge https://github.com/piwik/developer-documentation/pull/51