ENH: Lookup launcher and default settings files based on application name

Since following r24004 (ENH: Allow application name to be defined by
argv0) , we are sure the application name is set appropriately.
This commit will also ensure the application executable will lookup
launcher and default settings files based on the application name.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24119 3bd1e089-480b-0410-8dfb-8563597acbee