BUG: Fix generation of additional launcher settings

This commit ensures the file doesn't include extra spaces. These
were causing problem when parsing setting file using ConfigParser
python module used in slicer_wiki_extension_module_listing.py [1]

[1] https://github.com/Slicer/slicer-wiki-scripts/blob/ee52ed3b08346c04a3e2e09a309bae7f33578e4f/slicer_wiki_extension_module_listing.py#L728-L757

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24174 3bd1e089-480b-0410-8dfb-8563597acbee