MODE-1761 Added debug and trace logging to sequencing operations

Added debug logging for 'org.modeshape.jcr.sequencing' that outputs
the initialization of each sequencer (with valid path expressions)
and each invocation of a sequencer.

Added more trace logging for 'org.modeshape.jcr.sequencing' that
outputs very details messages describing the various activities
(and exit points) of sequencing.

Note that unconventional log names were used to make it easier
to enable and disale all logging for sequencing.