add ConcurrentUtil.newScheduledThreadPoolExecutor

Use helper factory method to create ScheduledThreadPoolExecutors
(related to jPOS-102 (https://jpos.org/issues/issue/jPOS-102)
added helper getScheduledThreadPoolExecutor
jPOS-102 use ScheduledThreadPoolExecutor

use ScheduledThreadPoolExecutor instead of Timer
This makes the code more readable, specially in the work-around
a race condition where a response could arrive exactly at expiration
time, code is much more readable now using future.cancel.

Removed unused variable and jmx-doc stuff we are not using anymore.
Fixed javadoc
jPOS-55 make sure MTI is padded to 4 positions
jPOS-63 Filter sensitive in Context.dump

if entry key starts with an '*', we don't show it in dump.
expose participant info in Thread name

Sets the thread name with some hints about what a given session is doing
(preparing, committing, aborting a given participant). Could be useful
in thread dumps as provided by the SystemMonitor.