more flexibility in queued job batch files

[bernstei]

It would be useful to support more arbitrary queuing system header entries. Some times those need to replace one of the normal ones, like the node specification. Probably this can only generally implemented by replacing all the logic inside the queuing system python functions to a templating system. There will still be queuing system dependence because of the actual commands and parsing of the status queries, but the files may be better off entirely templated.