Make shared optical properties in SimulationData #86
Description
SimulationData currently assigns optical properties to each individual geometry element. This causes the exported JSON to be large, with repeated optical properties for every element. It also makes it difficult to tweak optical properties shared by multiple elements (i.e. change reflectivity of every heliostat).
Can we change SimulationData to store optical properties somewhere, then elements are assigned an identifier that relates to specific shared optical properties? Legacy soltrace used strings to match elements to optical properties.