honor run option with a default maze of 30x30

default_args in project
Display.main()
  if argument is empty ignore it
  if file read fails, exit
add a WHEREWHAT file
extract MazeParamEditor to share it, prepare for having a GUI instead of console

project_params

@@ -4,3 +4,4 @@ project_basedir=$(pwd)
 project_mainpackage=org.artisanlogiciel.games
 project_mainclass=$project_mainpackage.Display
 project_version=0.0.1
+default_args='lab/lab30x30.raw'