Implement python logic tree parser (in nrml format)

[Anton Gritsay]

Example logic tree files: https://github.com/monellid/logicTree

[Anton Gritsay (angri)]

So far parsing and checking of both logic trees is done and tested, new code still needs to be documented though. What's left is processing of logic trees (sampling, iterating and enforcing "a-b-mMin-mMag" corellation) and plugging that all in to the project instead of legacy java implementation.

Everything's been working on is here: https://github.com/angri/openquake/commits/logic-tree

[Anton Gritsay (angri)]

Pull request: https://github.com/gem/openquake/pull/539

[Anton Gritsay (angri)]

Blackbox test for new logic tree processor needs to be implemented. "Incomplete" until the test data is available.

[Anton Gritsay (angri)]

Here are relative uncertainties blackbox test data files - input data (source model and a logic tree) and all possible results.

[Anton Gritsay (angri)]

Merged upstream in 1492ded103a51f982c5bec9a5b58ee59fa787c3d