* DEV: move sidebar community section to database
Before, community section was hard-coded. In the future, we are planning to allow admins to edit it. Therefore, it has to be moved to database to `custom_sections` table.
Few steps and simplifications has to be made:
- custom section was hidden behind `enable_custom_sidebar_sections` feature flag. It has to be deleted so all forums, see community section;
- migration to add `section_type` column to sidebar section to show it is a special type;
- migration to add `segment` column to sidebar links to determine if link should be displayed in primary section or in more section;
- simplify more section to have one level only (secondary section links are merged);
- ensure that links like `everything` are correctly tracking state;
- make user an anonymous links position consistence. For example, from now on `faq` link for user and anonymous is visible in more tab;
- delete old community-section template.
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