pool: Clean up StorageClassContainer and StorageClassInfo

- Addresses catch all exception handlers

- Removes redundant locking in StorageClassContainer

- Removes unused fields

- Addresses synchronization issues

- Rewrites shell commands as annotated commands (better help output,
  better tab completion in the future).

- Drops deprecated 'define class' command (needs to be mentioned
  in release notes).

- Use thread pool rather creating new threads on every callback

- Avoid unnecessary collection copies

Target: trunk
Require-book: no
Require-notes: yes
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: http://rb.dcache.org/r/5468/