EvCustomer model does not propagate storage state across boot-sim boundary

[jecollins]

As a consequence, all instances start a sim session with completely empty batteries. Until this is fixed, there will be a startup-effect for this customer model that must be accounted for in game analysis. This problem is complicated by the fact that storage state is maintained per-subscription, and the model may end a boot session with multiple subscriptions depending on the specifics of tariffs available in the boot environment.

Ideally, the storage states from all current subscriptions at the time of recording the boot record will need to be consolidated in the boot record, then re-loaded and assigned to the initial subscription from the default broker at the start of a sim session.

[jecollins]

As a result of #1154, we have removed evcustomer from the standard config. This is now a low-priority issue.