Update CodeMirror Documentation

I wish I could have added tiddlers to the documentation in order to put the mini-tutorials in tabs but I couldn't.
So it is a bit messy in my opinion, but I think it is a good start.

I have tested every configuration with Tiddlywiki v 5.1.4.
Bootstrap fr-FR edition with a few dozens of translated tiddlers
fr-FR-server configured to serve the fr-FR edition
Integration of @evolena work into the fr-FR edition
Doc: How to Add A Menu to the Sidebar

This item is tagged so as to appear under Customise TiddlyWiki.
Transcluding information re Sidebar Menus

Transcluding information from newly proposed tiddler "How to Add A Menu to the Sidebar". This should help users discover ways in which to use the TOC macro.
Merge remote-tracking branch 'upstream/master' into fred
new buttons, exporter texts
Overriding of a few system tiddlers for fr-FR edition
Various updates to doc tiddlers in fr-FR edition
Corrections to overriden system tiddlers in fr-FR edition
plus new translated tiddlers
Create Page and tiddler layout customisation.tid
Update cla-individual.md
Update export button to use tiddler title as filename base
Merge pull request #1115 from inmysocks/patch-2

Update cla-individual.md
Add hooks mechanism and th-opening-default-tiddlers-list hook

see: https://github.com/Jermolene/TiddlyWiki5/issues/1064
Tweaked default tag background
add /dev docs
Remove alert from addHook.

Thanks to @tobibeer
Resources updates