Update DB to version 18: Machines can have an arbitrary number of memories,

so use an interconnection table, `memory_by_machine`.

Cicm.Database/Schemas/Machine.cs

@@ -55,16 +55,10 @@ namespace Cicm.Database.Schemas
         public int Id;
         /// <summary>Model name</summary>
         public string Model;
-        /// <summary>Size in kibibytes of program RAM</summary>
-        public int Ram;
         /// <summary>Resolution in WxH pixels</summary>
         public string Resolution;
-        /// <summary>Size in kibibytes of firmware</summary>
-        public int Rom;
         /// <summary>Machine type</summary>
         public MachineType Type;
-        /// <summary>Size in kibibytes for video RAM</summary>
-        public int Vram;
         /// <summary>Introduction date, 0 if unknown, 1000 if prototype</summary>
         public int Year;
     }