Separate random data generation from random data retrieval

[willu47]

I'm interested in using the PuLP version of OSeMOSYS to run a global sensitivity analysis. This involves running a pre-prepared sample through the model.

I believe that this could be accommodated if the calls to generateRandomData were replaced within a look-up function, which retrieves the sample of random data for the current iteration (i) for the particular parameter.

The random sample could then be generated via a number of different approaches, and thus enable different analysis approaches of the results.