link the aggregate_wl and incorporate event type in the LossesBase

[sahand-asgarpour]

In the LossesBase, EV1 is hard-coded, while multiple event-based hazard maps can be introduce, or multiple hazard maps wih return-periods can be input. Hence, the LossesBase can not currently handle these situations.

Moreover, aggregate_wl is linked to analysis_config_data while this exists in the network_config_data.

So link the aggregate_wl to the network_config_data and incorporate event type (RP, or EV) in the LossesBase.