Add option to define number of samples?

[stufraser1]

• Add option to define the number of sample run per scenario, with a reasonable upper limit for computing requirements
• Improve description / purpose of sample, and how the losses differ to those run under 'analytical' run. Users are going to be surprised by seeing option of 10 samples on the output page (not set by them) so we either need to state 10 samples will be run, or offer a choice, and reason why / potential effect they'll see.

[vinulw]

#43 adds number of samples field in the Run Analysis section