spacemanager: Do not use ThreadManager

Space manager uses a regular Java thread pool instead. Introduces
the following new configuration property:

spacemanager.limits.threads=30

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Paul Millar <paul.millar@desy.de>
Acked-by: Dmitry Litvintsev <litvinse@fnal.gov>
Patch: http://rb.dcache.org/r/6376/