Convert Settings screen to HTML, and move to Tab

[RealRaven2000]

In order to be future proof, but also to simplify moving it into a tab, we need to start converting the xhtml / xul based settings screen into plain HTML. This is necessary to make SmartTemplates more compatible with Thunderbird 115 and newer versions as XUL and related layout rules are gradually removed in Thunderbird Core.

Problems

• at the moment the settings screen is complicated and has 2 side-by side parts. It already had problems based on using flex, this needs to be redesigned
• the variables tab needs to be recoded in a way that it can also be used within Composer
• the account templates area uses cloning to generate the different identities; this needs to be redone in HTML
• some parts of the settings (such as the license tab) do not need to share half the screen with account settings. Only show components of the "right hand side" with the account settings where it makes sense.

[RealRaven2000]

So far, some users have made pretty dreadful experiences with the settings dialog in Thunderbid 115, so this issue must be escalated to become the next most important thing. It will be very hard to do without breaking everything, converting the Settings for QuickFolders was a nightmare and took several weeks.

I am pinning this issue to the top three now.

[RealRaven2000]

Working on the preview, it doesn't functionally work yet but you can preview the layout via the test menu:

smartTemplate-fx-4.5.1pre11.zip

here is a preview of the very first page. I have to completely rewrite the code that clones this deck for each of the identities so I can fill the dropdown.