Tab Groups 1.5.0

A big one, mostly thanks to @sinazadeh, whose PR #4 added the options asked for in #2.

New

• Colored backgrounds behind a section's header, its tabs, both, or the whole section as one block. A slider sets how strong the color is.
• One color for every section, if you'd rather not use each site's own color.
• Text turns lighter or darker on its own when it would be hard to read on a color. You can switch this off.
• More ideas: a fold-out with AI, Shopping, News, Work, Coding, Music, Gaming and Banking packs. Search (DuckDuckGo, Bing, Brave Search, Ecosia and more) is the new first idea.
• Group from N tabs: a section only forms once that many of its tabs are open. Each section can set its own number.
• Sections per space: keep a section to some spaces, from the settings page or the header's "Only in this space".
• The header button can Clear, Unload (keeps the tabs, frees their memory) or be hidden.
• Indent a section's tabs, draw a line along them, hide the header line, and pick when the tab count shows.
• Backup and restore your sections and options from the settings page.

Smaller changes

• Zen's Clear button can sit on the divider below your sections, where it closes only the loose tabs. Top, divider or both.
• The settings page is split into Appearance and Behavior and keeps up with changes made in Sine's options box.
• Tab Groups' items in the tab right-click menu can be switched off.

Fixes

• Header colors could stay blank on a new profile. The color cache rebuilds once after updating.
• The collapse arrow was black instead of the text color.
• A tab pinned out of a folded section, or moved into a folder or split view, stayed hidden.

Tested on Windows with Zen 1.23.3b through Sine. Full list in CHANGELOG.md.