xrootd, pinmanager, dcap, gplazma, admin, pool, poolmanager, pnfsmanager, webdav, cleaner: Add documentation and other minor property adjustments

Renamed xrootd.threads to xrootd.limits.threads.

Added time unit handling to MovePinRequestProcessor.

Renamed poolmanager.cache-hit-messages.enabled to
poolmanager.enable.cache-hit-message.

Renamed pinmanager.max-pin-duration to pinmanager.limits.pin-duration.

Renamed pool.cell.wait-for-files to pool.wait-for-files.

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/5855/