In a SQL server 2016 the database, in it table Poss has been created. Some records are created. In a Visual Studio 2015 the project has been created, in it there was a reversal to table Poss using Entity Framework. After reversal representation showed a record count in Poss = 0 and in the Database there was table Pos and a folder dbo. __ MigrationHistory. What for this folder is necessary?