Conform to sibling requirements

desktop/js8call.desktop

@@ -2,7 +2,7 @@
 Name=JS8Call
 Comment=Ham Radio real time chat over HF
 Exec=$HOME/.local/bin/JS8Call
-Icon=$HOME/.local/share/HamPack/desktop/icons/js8call_icon.png
+Icon=$HAMPACK_DIR/desktop/icons/js8call_icon.png
 Type=Application
 Categories=HamRadio;Utility;
 Terminal=false

desktop/potacat.desktop

@@ -2,7 +2,7 @@
 Name=POTACAT
 Comment=Amateur radio spot aggregator with CAT control, QSO logging, and panadapter integration
 Exec=$HOME/.local/bin/POTACAT.AppImage
-Icon=$HOME/.local/share/HamPack/desktop/icons/potacat.png
+Icon=$HAMPACK_DIR/desktop/icons/potacat.png
 Type=Application
 Categories=HamRadio;Utility;
 Terminal=false

desktop/qttermtcp.desktop

@@ -2,7 +2,7 @@
 Name=QtTermTCP
 Comment=TCP Terminal
 Exec=$HOME/.local/bin/QtTermTCP
-Icon=$HOME/.local/share/HamPack/desktop/icons/qttermtcp.png
+Icon=$HAMPACK_DIR/desktop/icons/qttermtcp.png
 Type=Application
 Categories=HamRadio;Utility;
 Terminal=false

desktop/yaac.desktop

@@ -2,7 +2,7 @@
 Name=YAAC
 Comment=Yet another aprs client
 Exec=java -jar $HOME/.local/bin/yaac/YAAC.jar
-Icon=$HOME/.local/share/HamPack/desktop/icons/yaaclogo.png
+Icon=$HAMPACK_DIR/desktop/icons/yaaclogo.png
 Type=Application
 Categories=HamRadio;Utility;
 Terminal=false