User experience improvements, including settings.
- Add settings page with base settings for dark mode, clean interface, and breadcrumbs.
- Change breadcrumb icon to an arrow to make it clearer that it is navigation history, not structure of the site.
- Make backend changes to improve notification handling.
- Simplify main navigation bar.
- Correct failure to highlight active Security Tools in main navigation bar.
- Remodel homepage.
- Improve security through implementation of secure headers.
[No API changes]