Interface > Message: add support for marking messages as "do not log"

Some status updates (e.g. image downloads) display a plethora of
messages en route to completion.  By making the final entry of the
ParamArray "DONOTLOG", PD's central messager can now be told to not
relay such messages to the debugger.

As always, conditional compilation tags are used to completely remove
this code when the program is compiled in a non-debug mode.