This fairly extensive commit in terms of the number of affected
classes but relatively small conceptually. It is a refactoring of the
LoggingEvent class. The LoggingEvent class now implements the
ILoggingEvent interface which essentially contains getter methods with
no setters.  LoggingEvent is no longer serializable because the
relavant serialization code has been moved into LoggingEventSDO. A
LoggingEvent object now requires transformation into LoggingEventSDO
object before serializaiton. LoggingEventSDO class implements the
ILoggingEvent interface. SDO stands for Serialable Data Object.

All logback-classic components, including appenders, layouts,
converters now operate on ILoggingEvent instances. In other words,
logback-classic module is now a specialized processing chain for
ILoggingEvent objects, instead of LoggerEvent objects previously.

The getStartTime method which was previously part of LoggingEvent has
migrated to the Context interface. This change is a nice fit from a
conceptual point of view.

All tests pass. Performance is has not been degraded. 

In the future commits, the LoggerRemoteView may be renamed as
LoggerSDO, and similarly, LoggerContextRemoteView as LoggerContextSDO.