[WIP] - Update sims

[TomDonoghue]

To address:

• Mixing of linear and log10 scale in gen_power_spectrum #240 (linear vs log spaced values)
• how values are added together
• managing mode definitions and parameter values (SimParams, and relationship to sim transforms)

Note: there is a quirk with having both gen_power_values and gen_model which both generate model component and combine them together, but differently.