SSP-2305 Per-batch Hibernate sessions for external person sync

Conflicts:
	src/main/java/org/jasig/ssp/service/impl/ScheduledTaskWrapperServiceImpl.java

This was a cherry-pick from rel-2-2-patches. The conflicts were caused by
a feature add in the target branch (rel-2-3-patches) that changed method
signature in ScheduledTaskWrapperServiceImpl to support embedding task
names in background thread names.