Currently help menu item is the only external link in the CMS and the ability for it to work is hardcoded in the template. This request makes the target attribute definable by CMSMenu::add_link().
Adds documentation for how to add a basic external link to the CMS.
Add optional custom menu icons to the CMS main menu for every class
extending LeftAndMain (ModelAdmin). Works by setting optional static
$menu_icon = '/path/to/image' and providing custom styling for added
icons. Works for the menu as well as icon in the right-side (GridField) pane header.