Retract change to new tiddler handling in navigator.js

Original commit: d5c31ed07f31164cb2c2739ea56e7708fc39e9a4
Docs updates
Docs updates
Docs updates
Set release date for 5.0.8
Version number update for 5.0.8-beta
Prepare for 5.0.9-prerelease
Add @buggj's plugin site to the Community tiddler
Add docs for tw-close-other-tiddlers message

Fixes #461
Improve the descriptive text for missing tiddlers

Now we explain that it’s a missing tiddler, and add a “create” button
Docs update
Add docs for keyboard widget
Force the highlight language to lower case
Allow middle mouse button to trigger navigation suppression when clicking a tiddler link

Equivalent to holding control/command while clicking.