Provide simpler ScheduledTasks API

[tsteur]

As part of our "convention over configuration" strategy we want to simplify the ScheduledTasks API. Currently you need to know how hooks/events work, you need to know about the details of 2 or 3 classes and how to handle them etc. In addition the plugin class gets bloated. Goal is to make it super easy but still provide huge flexibility and possibility for refactorings.

If possible provide a console generate command for scheduled tasks.

If - and only if - useful we could let people automatically execute the tasks via command line as well. The method name would be the command such as ./console tasks:privacymanager:deleteReportData. Via reflection we could automatically detect a possibly needed parameter and documentation. This is just an idea I don't think it is useful right now or is it? Just saying it is possible :)

[tsteur]

In 3e03b0a: refs #5301 started to simplify scheduled tasks API while staying backwards compatible

[tsteur]

In 756d1e0: refs #5301 added scheduled task generator, some code tweaks and more docs

[tsteur]

In e65e378: refs #5301 this should fix the scheduledreports tests

[tsteur]

In 5ac85b1: refs #5301 doc for plugin/tasks class

[tsteur]

In b457fcc: refs #5301 make sure to pass the instance to ScheduledTasks and not the className. Otherwise it is called statically. The disadvantage of this way is all task will be stored under the name "Tasks.$methodName" which can lead to naming collisions very quickly if it is not already the case. I am wondering why we keep only the last part of the class name and not the full namespaced class name here: https://github.com/piwik/piwik/blob/master/core/ScheduledTask.php#L105 ? Keeping the namespace would fix the naming collision. If we change to full namespace it could be possible a scheduled task is not executed once as the name changes

[tsteur]

Just noticed as the name of the task has already changed due to the refactoring we could easily change the behaviour of https://github.com/piwik/piwik/blob/master/core/ScheduledTask.php#L105 and use the full namespaced name as long as there are no objections?

[mattab]

+1 to use full namespace to avoid collisions!

[tsteur]

In 89e8f8e: refs #5301 to prevent naming collisions use the full class namespace