Collaborators have write access as default, and can be changed via repository
collaboration settings page to change between read, write and admin.

- Allow to delete current avatar

Use hand-written SQL to do complex query

- Remove unused config settings `[picture] service`

Improve test cases, config settings, also show SSH config settings on admin config panel.

This is feature is workaround for #2628 (JumpCloud) and some other services
that allow LDAP search only under BindDN user account, but not allow any LDAP
search query in logged user DN context.

Such approach is an alternative to minimal permissions security pattern for
BindDN user.

- Update locales

- User profile un/follow
- List user's followers/following