Call DriverManager.registerDriver() only once on startup

As of JDBC Spec, a java.sql.Driver must register itself at the Drivermanager:

9.2 The Driver Interface
JDBC drivers must implement the Driver interface, and the implementation must
contain a static initializer that will be called when the driver is loaded. This initializer registers a new instance of itself with the DriverManager, as shown in CODE EXAMPLE 9-1

public class AcmeJdbcDriver implements java.sql.Driver {
  static {
    java.sql.DriverManager.registerDriver(new AcmeJdbcDriver());
  }
...
}

CODE EXAMPLE 9-1
Example static initializer for a driver implementing java.sql.Driver

When a Driver implementation is loaded, the static initializer will automatically
register an instance of the driver.

But since we have to deal with different, reloadable applications (appNG and appNGizer), we should register the Driver once when starting those.