Added the Connector class for connecting to the database. When the object is initialized, a connection to the database occurs, the destructor closes the connection
A DBConnector middleware connector has been added to pass an object of the Connector class, as an argument, to the handler.
Added a procedure for executing an SQL query to add users to the "users" table
Now, when processing the /start and /help commands, the user is added to the "users" table, if the user was added earlier, his name is updated
Closes #21