[Patch] Update commandline usage

[simon04]

Update commandline usage to include changes from r11162. Also output platform default directories.

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options provided as Java system properties:
	-Djosm.dir.name=JOSM                      Change the JOSM directory name

	-Djosm.pref=/PATH/TO/JOSM/PREF            Set the preferences directory
	                                          Default: /home/simon/.josm

	-Djosm.userdata=/PATH/TO/JOSM/USERDATA    Set the user data directory
	                                          Default: /home/simon/.josm

	-Djosm.cache=/PATH/TO/JOSM/CACHE          Set the cache directory
	                                          Default: /home/simon/.josm/cache

	-Djosm.home=/PATH/TO/JOSM/HOMEDIR         Set the preferences+data+cache directory (cache directory will be josm.home/cache

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