This is a JCommander-annotated class that holds parameters for OTP stand-alone mode.
These parameters can be parsed from the command line, or provided in a file using Jcommander's
at-symbol syntax (see http://jcommander.org/#Syntax). When stand-alone OTP is started as a
daemon, parameters are loaded from such a file, located by default in '/etc/opentripplanner.cfg'.
Note that JCommander-annotated parameters can be any type that can be constructed from a string.
This module also contains classes for validating parameters.
Some parameter fields are not initialized so when inferring other parameters, we can check for
null and see whether they were specified on the command line.