Remove started sharing notifications where the contact doesn't exist

Fix misplaced publisher prefill on tags page

Remove stream title from main stream

Move notifications and conversations links in collapsed header on small devices

Fix stream shortcuts on small screens

Use Person.by_account_identifier to find the author

Use https for the pod_uri if require_ssl is true

Before #6873 we deleted contacts when someone blocks a person, but we
didn't drop the notification for the started sharing event. In #6864
we try to get the contact for the notification, which is not there
anymore.

So we need to remove the notifications for the contacts that don't exit
anymore.

don't add the root author to the subscribers if the root post was deleted

* Adds a new metadata helper and methods to PostPresenter to have metas on post pages.

* Adds tests to post controller to check correctness of metas

* Add methods to PersonPresenter to have metas on profile pages

* Correct meta data helper test

* Update PersonPresenter, add test to PeopleController

* Creates TagPresenter. Display tag metas on tag index page

* Updata meta data helper spec

* Not displaying bio as the description meta on profile page for now. Privacy concerns to be cleared.

* Set meta info as hashes in presenters

* Move original hardcoded metas info to config/defaults.yml

* metas_tags include by default the general metas, update views

* Update code style, clean views

* Renames TagPresenter StreamTagPresenter, updates TagController spec

* Add a default_metas entry to diaspora.yml.example

* Align metas hash in presenters, refactor meta data helper

* Use bio as description meta if user has a public profile

* Rename StreamTagPresenter to TagStreamPresenter

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