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/autoload/org-export.el

@@ -1,5 +1,4 @@
 ;;; lang/org/autoload/org-export.el -*- lexical-binding: t; -*-
-;;;###if (featurep! +export)
 
 (defun +org--yank-html-buffer (buffer)
   (with-current-buffer buffer