Create Settings article

[wsmwk]

Model on https://support.mozilla.org/en-US/kb/firefox-options-preferences-and-settings
Related to thunderbird/thunderbird-website#1198

Possible Links to other articles:

• Config editor
• Account Settings
• Account Hub?
• Layout
• Search types
• Languages if it exists
• Spam
• Encryption
• Add-ons & Themes

[wsmwk]

Information can also be gotten from https://support.mozilla.org/en-US/kb/advanced-panel-settings-in-thunderbird

But it's very old, so perhaps we retire that article after completing the new one. And fix up the items that point to the old article.