Add meta field to JobArgSpec

[richcar58]

Add a "meta" field of type String to the JobArgSpec. This will allow users to attach any data they choose to a job request's AppArgs, ContainerArgs and SchedulerOptions inputs. A similar field will be added to AppArgSpec to allow meta information to be attached to an application. Meta content in a job request overrides that in an application definition when both are present. If meta is not assigned in a job request, the job inherits the meta content from its application if any exists.