Parameter model

This is out of date as of #601

Artemis employs a parameter model which is separated into external and internal parts, with a conversion between them. The decision to implement it this way is because the internal organisation is impacted by which parameters are needed for executing certain functions, which may not correspond directly to a logical way of specifying instructions for artemis to run an experiment. For example, the wavelength, resolution, and beam size are internally referred to as "ISPyB" parameters, because they are needed for making IPSyB depositions. However, these values are logically best considered as experiment parameters.

Externally supplied parameters are validated against a strict JSON schema, with a version tag, in order to reduce the chance of executing the wrong instructions.