* feat: ctrl+tab cycles within essential/workspace tabs only
* add test for ctrl+tab cycling by attribute
* move settings UI related code to /src/zen, revert patches for main.inc.xhtml and main.js, use simple tab filter when current tab is hidden
* chore: Cleanup and add extra pref, b=no-bug, c=tests, tabs
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Co-authored-by: mr. m <mr.m@tuta.com>
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