ui: added universal font size setting and shortcuts for changing it

This change adds font size and font family to the ApplicationSettings to have a single point for manipulating them. The
font size can also be changed via the menu or the zoomIn and zoomOut shortcuts on all platforms.

src/lib/component/view/GraphViewStyleImpl.h

@@ -7,6 +7,7 @@ class GraphViewStyleImpl
 {
 public:
 	virtual float getCharWidthForNodeType(Node::NodeType type) = 0;
+	virtual float getCharHeightForNodeType(Node::NodeType type) = 0;
 };
 
 #endif // GRAPH_VIEW_STYLE_IMPL_H