Refactor model creation

- Retire Full model in favor BlockFull 
- Go directly to look-up table instead of via pods
- create pods from look-up table if needed
- consider complicated models (multislice, ptycho-tomo) when designing the new look-up table
- consider splitting the data loading from the main process
- revisit current paradigm that every rank knows everything - find way to move data between ranks.
