Use pixels to specify the font sizes

Basically reverts the last font related commits since pointSize isn't
as reliable as pixelSize.

Also some layout values (margins, spacings) have been moved out to Config.h.

include/ui/Menu.h

@@ -2,13 +2,18 @@
 
 #include <QMenu>
 
+#include "Config.h"
+
 class Menu : public QMenu
 {
 public:
 	Menu(QWidget *parent = nullptr)
 	    : QMenu(parent)
 	{
-		setFont(QFont("Open Sans", 10));
+		QFont font;
+		font.setPixelSize(conf::fontSize);
+
+		setFont(font);
 		setStyleSheet(
 			"QMenu { color: black; background-color: white; margin: 0px;}"
 			"QMenu::item { color: black; padding: 7px 20px; border: 1px solid transparent; margin: 2px 0px; }"