[desktop] correcting category for desktop file
Renaming desktop/ dir to applications/

This seems to match what is expected by the gnome desktop standard
Desktop files are now in usr/share/applications
Renaming applications/ dir to usr/share/applications
[rpm] hopefully packaging .desktop file correctly now
[icons] moving 256x256 icon into standard hicolor apps dir
Removing 512x512 icon
[MANIFEST] putting icon in standardised directory
[rpm] now installing the icon
[rpm] using US spelling in Summary field
Renaming gen_nodes_file to pbs_gen_nodes_file

This change was requested by Orion Poplawski as part of accepting pbsclusterviz into Fedora