Added schemas and validators to Config

Details:
* For every Config there is a schema of type Object named with the
  _SCHEMA suffix (e.g., TOPOLOGY_WORKERS_SCHEMA)
* For simple Classes (String, Number, Boolean), just the Class is
  sufficient for the schema's value
* For other Classes, instances of the FieldValidator interface are used.
* FieldValidator declares a method to validate the field and a method to
  return a plain-language description of the criteria for the user.

Status: Compiles, but not tested.  Nothing makes use of the schemas yet.
Make messaging config Strings final
Fix white-space in Config
Remove unknown topology.acker.tasks config
Correct a few config schemas
Use schemas to check storm config/proof-of-concept
Move validators to own file, add tests

Other cosmetic changes.
Merge remote branch 'marz/master' into add-config-schema-validation

Conflicts:
	conf/defaults.yaml
	storm-core/src/jvm/backtype/storm/Config.java
update changelog