Sanitisation of input data

[jamesturner246]

The whole model loading core in model_parser could do with a rethink, to test that both the main config file -- e.g. France.Config.json -- has sensible values and if fully defined. Same for the static and dynamic risk factor configs -- e.g. France.HLM.json and France.NewEBM.json.

Furthermore, we should check that the data is complete over defined ranges. For example, if max age is defined as x, we should ensure that all age dependent data is defined up to at least x.

The code should fail on any missing data, and any missing files -- it often just carries on silently/with a warning message.

[alexdewar]

Waiting for #166 to be finished before starting on this.