Resolving bugs in classes:
DatabaseManager -> login - if there is no row in local database about user, select command from server is commited.
DatabaseManager -> insert - when checking if the data already exist in the database, row variable is modified to be a parameter for select command.
AbstractManager -> remove (1 i 2) after removing from database, the data is now also removed from lists in program
DataVector -> (other classes) -> calculations module is modified to a module of a user preference calculation
AbstractManager - two abstract methods to load and refresh data were added.