Add .stow, remove .gitignore

A second stow directory was added to store secret files that should not
end up on Github. Both stow directories need to have a .stow file so
they know about and don't interfere with each other.

The .gitignore content is no longer needed since only the
.emacs.d/init.el is managed by stow, not the whole directory.
[camlistore] Set correct path to gpg secret ring
[brew] Install youtube-dl
[emacs] Auto-save org-mode files, set refile targets

All org-mode files are auto-saved once a minute, to allow automatic git
commits (see package autocommit).

Add all agenda files to the list of refile targets.
[autocommit] Commit and push all org-mode files automatically

All org-mode files in the ~/org directory are automatically committed to
git every 5 minutes. If the network is reachable, changes are also
pulled and pushed from/to Gitlab.

The implementation as an infinite loop managed by runit instead of as a
cron job is ugly, but I didn't see a good way to manage the crontab with
stow and it has the benefit that all output is written to a (rotated) logfile.
[mjolnir] Add common temp files to .stow-local-ignore