Fix dragging floating containers / click handling

include/con.h

@@ -54,6 +54,13 @@ Con *con_get_fullscreen_con(Con *con);
  */
 bool con_is_floating(Con *con);
 
+/**
+ * Checks if the given container is either floating or inside some floating
+ * container. It returns the FLOATING_CON container.
+ *
+ */
+Con *con_inside_floating(Con *con);
+
 /**
  * Returns the container with the given client window ID or NULL if no such
  * container exists.