JBoss 7 Logging Modification for Async support

Modified the JBoss 7 Logging part: Using the JBoss-specific ExtLogRecord instead of JUL LogRecord.
Reason: The MDC/NDC implementation doesn't work for async logging (e.g. JBoss Built-In AsyncAppender) because the thread-context of MDC/NDC is lost in worker thread(s). 
JBoss ExtLogRecord has built-in support for getting MDC/NDC parts AND has a "copyAll" - method which copies thread-context specific things (like MDC) to the LogRecord. This method is also called on JBoss Built-in Async Appender.

With my modifications all MDC/NDC fields are now available in the Gelf-Message when using the AsyncAppender