Refactor out map.el usage

After some profiling, it turns out map-put and map-delete are 5-7x
slower (more on Emacs 25) than delq, setf/alist-get and add-to-list for
small lists (under 250 items), which is exactly how I've been using
them.

The only caveat is alist-get's signature is different on Emacs 25, thus
a polyfill is necessary in core-lib.

modules/lang/org/config.el

@@ -341,7 +341,7 @@ between the two."
 (defun +org|setup-hacks ()
   "Getting org to behave."
   ;; Don't open separate windows
-  (map-put org-link-frame-setup 'file #'find-file)
+  (setf (alist-get 'file org-link-frame-setup) #'find-file)
   ;; Let OS decide what to do with files when opened
   (setq org-file-apps
         `(("pdf" . default)