project file allow installation in another dir than "/usr"

E.g. this way I can build and install in "~/.local", or "/usr/local".

app/app.pro

@@ -19,20 +19,26 @@ RESOURCES += qml/resources.qrc
 ##              INSTALLS
 #########################################
 
-target.path += /usr/bin/
+PREFIX = $$(PREFIX) # Pass the make install PREFIX via environment variable. E.g. "PREFIX=/path/to/my/dir qmake".
+isEmpty(PREFIX) {
+    message(No prefix given. Using /usr.)
+    PREFIX=/usr
+}
+
+target.path = $$PREFIX/bin
 
 INSTALLS += target
 
 # Install icons
 unix {
     icon32.files = icons/32x32/cool-retro-term.png
-    icon32.path = /usr/share/icons/hicolor/32x32/apps
+    icon32.path = $$PREFIX/share/icons/hicolor/32x32/apps
     icon64.files = icons/64x64/cool-retro-term.png
-    icon64.path = /usr/share/icons/hicolor/64x64/apps
+    icon64.path = $$PREFIX/share/icons/hicolor/64x64/apps
     icon128.files = icons/128x128/cool-retro-term.png
-    icon128.path = /usr/share/icons/hicolor/128x128/apps
+    icon128.path = $$PREFIX/share/icons/hicolor/128x128/apps
     icon256.files = icons/256x256/cool-retro-term.png
-    icon256.path = /usr/share/icons/hicolor/256x256/apps
+    icon256.path = $$PREFIX/share/icons/hicolor/256x256/apps
 
     INSTALLS += icon32 icon64 icon128 icon256
 }

app/main.cpp

@@ -58,7 +58,6 @@ int main(int argc, char *argv[])
         cout << "  -p|--profile <prof> Run cool-retro-term with the given profile." << '\n';
         cout << "  -h|--help           Print this help." << '\n';
         cout << "  --verbose           Print additional information such as profiles and settings." << '\n';
-        cout << "  -v|--version        Print the program name and version." << '\n';
         return 0;
     }
 

app/qml/ApplicationSettings.qml

@@ -746,7 +746,7 @@ QtObject {
 
         loadCustomProfiles()
 
-        var profileArgPosition = args.indexOf(/-p|--profile/)
+        var profileArgPosition = args.indexOf("--profile")
         if (profileArgPosition !== -1) {
             var profileIndex = getProfileIndexByName(
                         args[profileArgPosition + 1])

cool-retro-term.pro

@@ -5,7 +5,17 @@ CONFIG += ordered
 SUBDIRS += qmltermwidget
 SUBDIRS += app
 
+#########################################
+##              INSTALLS
+#########################################
+
+PREFIX = $$(PREFIX) # Pass the make install PREFIX via environment variable. E.g. "PREFIX=/path/to/my/dir qmake".
+isEmpty(PREFIX) {
+    message(No prefix given. Using /usr.)
+    PREFIX=/usr
+}
+
 desktop.files += cool-retro-term.desktop
-desktop.path += /usr/share/applications
+desktop.path += $$PREFIX/share/applications
 
 INSTALLS += desktop