Rename efLogEvent to EventLogging::logEvent

* EventLogging::logEvent mirrors more closely the JavaScript API,
  mw.eventLog.logEvent, as pointed out by Matt Flaschen in his review of
  Ifa74cbd55
* To make that possible, add includes/EventLogging.php.
* Also move EventLogging.hooks.php -> includes/EventLoggingHooks.php, for
  consistency with other classes added by this extension.
* Not adding a backward-compat alias for efLogEvent because if this is merged
  relatively soon, efLogEvent will have not seen production usage.
* Some of the other global functions in EventLogging.php should be methods of
  the EventLogging class as well, but that's for another patch.

Change-Id: I7d0f7fa21c78ac0f8b2dc238ea881804f13c01d0
Merge "Rename efLogEvent to EventLogging::logEvent"