Create setting for default type of draft tiddlers

[michaeljmcd]

Adding a setting with the type to be used for new tiddlers so that this can be overridden for cases where some other type is desirable, as might be the case in a mostly-Markdown wiki. Also changes the setting in the Markdown Demo so that creating a tiddler off of a "missing tiddler" entry defaults to Markdown.

[github-actions]

Confirmed: michaeljmcd has already signed the Contributor License Agreement (see contributing.md)

[netlify]

✅ Deploy Preview for tiddlywiki-previews ready!

Name	Link
🔨 Latest commit	55cc5be
🔍 Latest deploy log	https://app.netlify.com/sites/tiddlywiki-previews/deploys/67463e761df0c20008f67296
😎 Deploy Preview	https://deploy-preview-8783--tiddlywiki-previews.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[pmario]

This setting is very similar to the New-Image "Hidden Setting": https://tiddlywiki.com/#Hidden%20Setting%3A%20New-Image%20Type

So you can clone this one and add it to the list. Since the setting is global it should be part of the core wiki info at tiddlywiki.com

The markdown-edition should also have some info about the new default setting. So users know what's going on.

May be the markdown-plugin "readme" may also have a link to the new Hidden Setting docs.

[michaeljmcd]

@pmario Good call-out on documentation, I've gone back and added notes in the places indicated.

[Jermolene]

Great thank you @michaeljmcd @pmario