status code specification / state enhancement

[jkrue]

To be really independent from the framework used by the JobProxy server, we must specify general status codes (and description) used by all frameworks. The BiBiServ defines an exhausted list of status codes/descriptions we could use for this purpose, e.g.:

Code	Description
600	task finished/completed
601	task submitted
602	task preprocessing
603	task pending
604	task running
700	general error / description is not a static string

See for complete list. For JobProxy we just need a few of them.

The state object could/should then provide two another properties like internal_statuscode and internal_statusdescription. However, this might be only useful for debugging ...