Feature/auto assign centroids (#640)

* assign centroids by default
set cover to the full value

* input data for San Salvador house assets
deleting cover values makes more sense

* CostBenefit.plot_waterfall: pydoc, add a note about arguments restriction
hazard and haz_future should have common centroids

Author: emanuel-schmid

climada/engine/cost_benefit.py

@@ -537,7 +537,8 @@ def plot_waterfall(hazard, entity, haz_future, ent_future,
         hazard : climada.Hazard
         entity : climada.Entity
         haz_future : Hazard
-            hazard in the future (future year provided at ent_future)
+            hazard in the future (future year provided at ent_future).
+            ``haz_future`` is expected to have the same centroids as ``hazard``.
         ent_future : climada.Entity
             entity in the future
         risk_func : func, optional
@@ -558,11 +559,11 @@ def plot_waterfall(hazard, entity, haz_future, ent_future,
         future_year = ent_future.exposures.ref_year
 
         imp = ImpactCalc(entity.exposures, entity.impact_funcs, hazard)\
-              .impact(assign_centroids=False)
+              .impact(assign_centroids=hazard.centr_exp_col not in entity.exposures.gdf)
         curr_risk = risk_func(imp)
 
         imp = ImpactCalc(ent_future.exposures, ent_future.impact_funcs, haz_future)\
-              .impact(assign_centroids=False)
+              .impact(assign_centroids=hazard.centr_exp_col not in ent_future.exposures.gdf)
         fut_risk = risk_func(imp)
 
         if not axis: