Generate fonts.qss dynamically during build

The static font size and weight looked odd on Mac OS.
QSS does not support different platform specific styles. Hence the platform
scopes had to be added to blackgui.pro and fonts.qss generated during
build process.

refs 936

src/blackgui/blackgui.pro

@@ -53,8 +53,23 @@ RESOURCES +=
 DESTDIR = $$DestRoot/lib
 DLLDESTDIR = $$DestRoot/bin
 
-OTHER_FILES += ./share/qss/*.qss ./share/qss/*.css ./share/qss/*.ini *.ico *.rc
-COPY_FILES += $$PWD/share/qss/*
+QSS_FONT_FAMILY = "Arial"
+QSS_FONT_SIZE = "8"
+QSS_FONT_STYLE = "normal"
+QSS_FONT_WEIGHT = "bold"
+
+macx {
+    QSS_FONT_SIZE = "12"
+    QSS_FONT_WEIGHT = "normal"
+}
+
+fontsqss.input = share/qss/fonts.qss.in
+fontsqss.output = $$DestRoot/share/qss/fonts.qss
+QMAKE_SUBSTITUTES += fontsqss
+
+OTHER_FILES += ./share/qss/*.qss ./share/qss/*.qss.in ./share/qss/*.css
+COPY_FILES += $$PWD/share/qss/*.qss
+COPY_FILES += $$PWD/share/qss/*.css
 
 win32 {
     dlltarget.path = $$PREFIX/bin

src/blackgui/share/qss/fonts.qss

@@ -1,7 +0,0 @@
-QWidget {
-    color: white;
-    font-family: "Arial";
-    font-size: 8pt;
-    font-style: normal;
-    font-weight: bold;
-}

src/blackgui/share/qss/fonts.qss.in

@@ -0,0 +1,7 @@
+QWidget {
+    color: white;
+    font-family: $$QSS_FONT_FAMILY;
+    font-size: $$QSS_FONT_SIZE pt;
+    font-style: $$QSS_FONT_STYLE;
+    font-weight: $$QSS_FONT_WEIGHT;
+}