Reduce indentation of nested replies

- Add yet another arrow in arrows-etcetera-gray.png
- Don't indent the :last-child reply
- Adjust arrow offsets and widths, for the :last-child reply
- When inserting a reply, update the parent-thread or
  previous-sibling, so the arrow to the new reply isn't broken
- Remove unnecessary .dw-svg-fake-varrow-hider-lo
Disable the SVG arrow renderer: it doesn't avoid deep indentation.
Add public/files/ softlink to parent Git repo

Assume there's a directory public-files/ in the parent repo, in which e.g. site
specific images can be placed.
Move www.debiki.com specific images away from this repo

Place them in my private debiki-site-www.debiki.com repo, and, for now only,
softlink their prevous locations in this repo to their new locations in the
debiki-site-www.debiki.com repo.
Move YoxView away from this repo

It's www.debiki.com specific. Place it in my debiki-site-www.debiki.com repo
instead, and, for now only, add a softlink to it.
Bump assets version link to /24/.
Remove duplicated database configuration from config files

Also make [the related Scala files that connects to the db] work with this.
Add hooks for LaTeX math support

- Add debiki.onEditPreviewShown and debiki.onPagePatched
- Run all <script type="text/x-debiki-config"> tags, roughly on page load

Now, websites can support LaTeX, via MathJax and the `html-scripts` config
param.
Bump assets version link to /26/.
Work around no "No" in user config post data.
Admin SPA: Use <ins> and <del> to show diffs on activity page.
Better diffs: Reduce edit cost.
Replace CodeMirror files with a submodule.
Add CodeMirror addon that shows Markdown line breaks.
Show Markdown line break also if > 2 trailing spaces.
Generate CodeMirror bundle, use version 3.13 not 2.x

Upgrade from CodeMirror 2.x to 3.x: Style .CodeMirror not .CodeMirror-scroll.
Use PostgreSQL data source, not BoneCP

There's some problem with BoneCP's connection pool, resulting in:
  java.sql.SQLException: Timed out waiting for a free available connection.
Bump assets version link to /27/.