`independantly` -> `independently`

Add new option for [General] process_new_segments_from option, 'segment_last_edit_time'. New option sets beginning of segments archiving from last edit time (or created time if it is found). Includes tests.

Add new RequestProcessor to Actions plugin for action detection + new RequestProcessor for ping request handling. Ping request handling is performed in new Heartbeat plugin. Also added a new method to Plugin, isTrackerPlugin for plugins to override if they are tracker plugins, but don't have a dimension or implement a tracker method.

As the plugin does now nothing anymore, I removed it.

Fixes #7759 Always enable the Diagnostics and Monolog plugins to make sure their DI config is always loaded

implement what's documented in FAQ and config file which was not actually implemented
fixes #7626

refs #5099

Fixes #7223, add new INI option [General] process_new_segments_from that controls the start date of archiving for segments that have not been archived before. If a creation date cannot be found, now is used.

HTTP will be used if (and only if) HTTPS is not supported at all (e.g. openssl is not installed or fopen/curl is not supported). If HTTPS is supported, we try to update through HTTPS: any failure will stop the update process and we don't fallback to HTTP. This is the expected behavior: a failure could be a MITM attack.

- Piwik will update over HTTPS if curl is supported
- the system check verifies that updating over HTTPS is supported (= curl supported)

I also replaced the check that does a request against Piwik to check
whether it is installed with `SettingsPiwik::isInstalled()` as discussed
recently

fixes #6895 - add a config option that causes the image graphs to show the evolution within the selected period instead of the evolution across the last n periods