Remove specs about services swallowing exceptions

Fix conversations autoSuggest showing non-mutual contacts

only create mentions after creating statusmessages

Fix backbone router for URLs with trailing slashes

Fixes the avatar on mobile multiphoto page

Fix aspect dropdown when person is being fetched

Refactor contacts page

Use diaspora_id validation from the federation gem

DRY

fetch mentioned people if they don't exist locally yet

Fixes #6979

fix #6989

Allow hovercards of remote people when not logged in

Improve /tag page performance.

In #6603 hovercards were activated for logged out users, but they only
worked for local people. Hovercards on remote-people are important to
get the diaspora-id to search the person on the local pod, if you don't
know who it is.

Cleanup old rake tasks

* accounts:run_deletions: was added with 0.4.0.0 two years ago for one-time usage.
* db:rebuild: db:reset does basically the same
* db:integration:preprare: the integration environments are not used.
* db:reset: there is a default db:reset, no need to write our own.
* db:drop_integration: the integration environments are not used.
* db:fix_diaspora_handle: really old migration from 2010
* db:move_private_key: also old migration from 2010
* maintenance:clear_carrierwave_temp_uploads: tmp/uploads doesn't exist anymore. And we have CleanCachedFiles as cronjob.
* maintenance:install_logrotate_config: diaspora has built-in logrotate support now, and people who want to use logrotate instead can write their own configs with the values they want.
* migrations:copy_hidden_share_visibilities_to_users: old migration from 2012
* migrations:invitations: legacy invitations were removed with #6976
* migrations:absolutify_image_references: old migration from 2010
* migrations:rewire_uppercase_hashtags: old migration from 2012
* migrations:remove_uppercase_hashtags: old migration from 2012

Don't create notifications from ignored people

Also move "shareable hidden"-logic to AlsoCommented, because it is the
only one that needs it. And write some specs for mentioned and started
sharing notifications.

Fixes #6294

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