lang/org: major refactor

The motivation for this change was to rethink lang/org's flags. Many of
its former flags represented non-features. Therefore, its flags have
been reduced to five: +dragndrop, +ipython, +pandoc, +gnuplot and
+present. Everything else is included as org-load-hooks and treated as
reasonable defaults.

Other changes:
- Fixes #1502: don't autopair certain pairs when in a math region
- Fixes #1483: broken localleader in org-agenda
- Adds gnuplot support #1108
- Doom's org submodules have been moved into lang/org/contrib/, because
  I expect there will be *many* more to come, and I don't want to
  pollute the moudle's root.

modules/lang/org/contrib/dragndrop.el

@@ -0,0 +1,39 @@
+;;; lang/org/contrib/dragndrop.el -*- lexical-binding: t; -*-
+
+(def-package! org-download
+  :commands (org-download-dnd org-download-dnd-base64)
+  :init
+  ;; Add these manually so that org-download is lazy-loaded...
+  (add-to-list 'dnd-protocol-alist '("^\\(https?\\|ftp\\|file\\|nfs\\):" . +org-dragndrop-download-dnd))
+  (add-to-list 'dnd-protocol-alist '("^data:" . org-download-dnd-base64))
+
+  (advice-add #'org-download-enable :override #'ignore)
+  :config
+  (setq org-download-image-dir org-attach-directory
+        org-download-heading-lvl nil
+        org-download-timestamp "_%Y%m%d_%H%M%S"
+        org-download-screenshot-method
+        (cond (IS-MAC "screencapture -i %s")
+              (IS-LINUX
+               (cond ((executable-find "maim")  "maim -s %s")
+                     ((executable-find "scrot") "scrot -s %s")))))
+
+  ;; Handle non-image files a little differently. Images should be inserted
+  ;; as-is, as image previews. Other files, like pdfs or zips, should be linked
+  ;; to, with an icon indicating the type of file.
+  (advice-add #'org-download-insert-link :override #'+org-dragndrop*insert-link)
+
+  (defun +org-dragndrop*download-subdir ()
+    (when (file-in-directory-p buffer-file-name org-directory)
+      (file-relative-name buffer-file-name org-directory)))
+
+  (defun +org-dragndrop*download-fullname (path)
+    "Write PATH relative to current file."
+    (let ((dir (or (if buffer-file-name (file-name-directory buffer-file-name))
+                   default-directory)))
+      (if (file-in-directory-p dir org-directory)
+          (file-relative-name path dir)
+        path)))
+  (advice-add #'org-download--dir-2 :override #'ignore)
+  (advice-add #'org-download--fullname
+              :filter-return #'+org-dragndrop*download-fullname))