Update to new icon files for UNIX style installs

src/syncterm/CMakeLists.txt

src/syncterm/GNUmakefile

src/syncterm/icons/generate-unix.sh

src/syncterm/syncterm.png

src/syncterm/syncterm16.png

src/syncterm/syncterm22.png

src/syncterm/syncterm24.png

src/syncterm/syncterm256.png

src/syncterm/syncterm32.png

src/syncterm/syncterm36.png

src/syncterm/syncterm48.png

src/syncterm/syncterm64.png