Make packaging for Flatpak easier (#57)

flameshot.pro

@@ -199,36 +199,38 @@ RESOURCES += \
 
 # installs
 unix:!macx {
-    packaging {
-        USRPATH = /usr
-    } else {
-        USRPATH = /usr/local
+    isEmpty(PREFIX) {
+      packaging {
+        PREFIX = /usr
+      } else {
+        PREFIX = /usr/local
+      }
     }
 
-    target.path = $${BASEDIR}$${USRPATH}/bin/
+    target.path = $${BASEDIR}$${PREFIX}/bin/
 
-    qmfile.path = $${BASEDIR}/usr/share/flameshot/translations/
+    qmfile.path = $${BASEDIR}$${PREFIX}/share/flameshot/translations/
     qmfile.files = $${TRANSLATIONS_FILES}
 
-    dbus.path = $${BASEDIR}/usr/share/dbus-1/interfaces/
+    dbus.path = $${BASEDIR}$${PREFIX}/share/dbus-1/interfaces/
     dbus.files = dbus/org.dharkael.Flameshot.xml
     
-    icon.path = $${BASEDIR}$${USRPATH}/share/icons/
+    icon.path = $${BASEDIR}$${PREFIX}/share/icons/
     icon.files = img/flameshot.png
 
-    completion.path = /usr/share/bash-completion/completions/
+    completion.path = $${BASEDIR}$${PREFIX}/share/bash-completion/completions/
     completion.files = docs/bash-completion/flameshot
 
-    desktopentry.path = $${BASEDIR}$${USRPATH}/share/applications
+    desktopentry.path = $${BASEDIR}$${PREFIX}/share/applications
     desktopentry.files = docs/desktopEntry/package/flameshot.desktop
 
-    desktopentryinit.path = $${BASEDIR}$${USRPATH}/share/applications
+    desktopentryinit.path = $${BASEDIR}$${PREFIX}/share/applications
     desktopentryinit.files = docs/desktopEntry/package/flameshot-init.desktop
 
-    desktopentryconfig.path = $${BASEDIR}$${USRPATH}/share/applications
+    desktopentryconfig.path = $${BASEDIR}$${PREFIX}/share/applications
     desktopentryconfig.files = docs/desktopEntry/package/flameshot-config.desktop
 
-    servicedbus.path = $${BASEDIR}/usr/share/dbus-1/services/
+    servicedbus.path = $${BASEDIR}$${PREFIX}/share/dbus-1/services/
     packaging {
         servicedbus.files = dbus/package/org.dharkael.Flameshot.service
     } else {