javadoc cleanup
Renamed BasicEntityDriverFactory to BasicEntityDriverManager
AddressableLocation now extends Location
NoMachinesAvailableException: deprecate Location field

- So that it will definitely be serialisable
Deprecate TaskStub
cleanup: incorporate review comments

- ExecutionManager returns immutable copies of task sets
- Tidy up some javadoc text
- Delete deprecated brooklyn.entity.ConfigKey (instead use 
  brooklyn.config.ConfigKey)
Merge pull request #609 from aledsage/fix/cleanup

Some cleanup (e.g. javadoc etc)