Adding new mdc field to LogEvent within a new args list. Related to #3671

* Field was moved from first to second args list for making the change backward compatible
* Defined implicit so that the second list doesn't need to be specified (existing code doesn't break)
* All changes to pattern matching against LogEvents were reverted
Improving Java API for getting logger. Related to #3671

* getLogger methods in Logging now receive callable
* Removing a lot of Option over-usage
* All changes to pattern matching against LogEvents were reverted