Get experiment 27 working again with the latest code.

[JackKelly]

• [x] #157
• [x] #158
• [x] Check that the satellite_processor and query_generators all make use of the modality-specific sun position
• [x] Use hrvsatellite_predicted.detach() in SatelliteTransformer.
• [x] Reshape so each timestep is seen as a separate example in HRVSatelliteProcessor
• [x] Remove random_timestep_indexes from plotting & validation code
• [x] Use the t0_idx provided by the data loader in the model code.
• [x] #159
• [x] #161