Update predictions loading process to include EMS

[meilinger]

An ems.csv file is available for loading into FireCARES. This file contains a count of predicted ems incidents that will occur per fire department.

We need to add a predicted number of ems incidents to the list of other predicted items in FireCARES: https://cl.ly/2cb3883b563f

See https://github.com/FireCARES/firecares/blob/master/firecares/firestation/management/commands/import-predictions.py for the current loading procedure for predictions. Note that EMS incident predictions are not specific to a particular structure hazard level so will need to be displayed across all hazard levels.