Check_MK Werk 5731: Custom icons and actions: Add new macro $USER_ID$

ID: 5731 Title: Custom icons and actions: Add new macro $USER_ID$ Component: Multisite Level: 1 Class: New feature Version: 1.5.0i3 The macro <tt>$USER_ID</tt> has been added to the replacement mechanic of "Custom icons and actions" URL. This macro is replaced with the ID of the user that is currently working with the GUI.