extend command line interface: keywords

[bastiK]

It would be useful to have access to certain JOSM features via command line, e.g. validation (#15182), projection, rendering (#15229). For this purpose, I suggest the following extended syntax:

java -jar josm.jar <keyword> <options> <args>

So for instance to use projection or rendering features, it would be

java -jar josm.jar projection -v +init=epsg:4326 +to +init=epsg:3857 <input.txt
java -jar josm.jar rendering -i data.osm --style style.mapcss --zoom 16 --box ... -o img.jpg

The current command line features are accessed with the josm keyword, which is the default and optional. Both of the following starts JOSM and opens the file track1.gpx:

java -jar josm.jar josm track1.gpx
java -jar josm.jar track1.gpx

If we have separate jar files for modules in the future, then you would simply drop the keyword:

java -jar josm-projection.jar -v +init=epsg:4326 +to +init=epsg:3857 <input.txt
java -jar josm-rendering.jar -i data.osm --style style.mapcss --zoom 16 --box ... -o img.jpg