Store local configuration in a separate file

The file is called `personal.el` and is not under version control
Add a dependency on `org-mode` for org-mode-crate.

org-mode-crate currently only works with org-mode release 7.9. It breaks
for new releases of org-mode. So I'm adding a dependency on org-mode and
anchoring org-mode to the right version until I can update my crate config