Descendants of this class should implement the {@link init()} method and call the
{@link makeSetting()} method to create a system setting for this plugin.
For an example, see {@link Piwik\Plugins\ExampleSettingsPlugin\SystemSettings}.
$systemSettings = new Piwik\Plugins\ExampleSettingsPlugin\SystemSettings(); // get instance via dependency injection
$systemSettings->yourSetting->getValue();