New: Removed Kpi and all its references

coscine/issues#2364

src/Database/Models/KpiModel.cs

-using Coscine.Database.DataModel;
-using Microsoft.EntityFrameworkCore;
-using System;
-
-namespace Coscine.Database.Models
-{
-    public class KpiModel : DatabaseModel<Kpi>
-    {
-        public override System.Linq.Expressions.Expression<Func<Kpi, Guid>> GetIdFromObject()
-        {
-            return (KpiObject) => KpiObject.Id;
-        }
-
-        public override DbSet<Kpi> GetITableFromDatabase(CoscineDB db)
-        {
-            return db.Kpis;
-        }
-
-        public override void SetObjectId(Kpi databaseObject, Guid id)
-        {
-            databaseObject.Id = id;
-        }
-
-        public int MarkAsSent(Kpi databaseObject)
-        {
-            databaseObject.SentSuccessfully = true;
-            return Update(databaseObject);
-        }
-    }
-}