Message Simulator improvements

Various improvements:

- Removed the application's ability to send multiple messages per broadcast. SimulatorController still has this ability via deprecated methods, but the application does not. It is a better practice to send one message at a time.

- The message frequency no longer has to be expressed in messages per second. Now users can choose messages per second, minute, hour, day, or week.

- Users can choose message fields whose value in outgoing messages will be overridden by the current date/time instead of whatever was in the XML file. On the command line, the time override fields are specified with the -o switch. In the GUI, a new checkbox list allows users to specify the time override fields and change them at any time while the simulator runs.

- Changed the verbose (-v) switch to a silent (-s) switch. Verbose output is now the default but can be disabled by passing the -s switch.

- Users can specify the UDP port for outgoing messages. On the command line, use the -p switch. In the GUI, a spin box lets users choose a UDP port.