Implement Batch cluster backend for Computation framework

[karlnapf]

@lambday has written first parts of a framework for parallel computation of independent tasks.

It allows to code against a very general interface, which then executes tasks in a serial/parallel/distributed fashion internally, based on the backend.

It is already used by his log-determinant GSoC 2013 project.

This task is to add a Batch cluster backend for it.

I have written a (working) draft in python which I successfully used for PBS and SGE. This is based on @lambday 's initial structure, though extended it a bit.
https://github.com/karlnapf/independent-jobs

The python framework is used from within here
https://github.com/karlnapf/ozone-roulette