Add focusWindow dispatcher. Takes titles & classes

Removed focusWindowByClass function, replaced with focusWindow.
Either takes a class matching regex, or a title matching one,
beginning with "title:"
Kept the focuswindowbyclass dispatcher identifier to stay backwards
compatible with existing configs.

src/managers/KeybindManager.hpp

@@ -61,7 +61,7 @@ private:
     static void         resizeActive(std::string);
     static void         moveActive(std::string);
     static void         circleNext(std::string);
-    static void         focusWindowByClass(std::string);
+    static void         focusWindow(std::string);
     static void         setSubmap(std::string);
 
     friend class CCompositor;