closes #7584

This was used for the old post fetching

Related to diaspora/diaspora_federation#31

closes #7085

* 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

move it to Diaspora::Federation::Entities and use it in some tests, but most of the tests can be removed later.

* find returns nil if nothing found
* find! raises errors if not found or not visible

this is not used anymore:
* not logged in users are redirected to the login page
* logged in users see the normal 404 page

* move presenters back to controllers, this is view-logic
* use PostService in CommentService
* remove iframe route, this is not used anymore
* id/guid limit at 16 chars, hex(8) is 16 chars long

Fix typos

change forbitten to forbidden

fix styling issue and copypaste

improve code style for aspec_memberships_controller.rb with rubocop

fix styling issues

aligned elements of hash literals

fix typo

fix locale name and styling of its usage

fix failing tests

closes #6554

closes #6533

closes #6490

Squashed commits:

[ada0f09] Remove favorites from Posts table

closes #6208

  - If a mention for the current user and the displayed post exists,
    mark it as read
  - Use set_read_state instead of manually setting unread as false

* Rename and reorganize post fetcher to fix autoloading, also let it use
  Faradays default connection so we get nice redirects
* Add initializer to load libs at a central place
* added lib dir to autoload_once paths to increase thread safety
* Moved lib/exceptions.rb to lib/diaspora/ to conform namespacing

strip last beta leftovers and fix syntax errors, travis is kinda down, lets hope nothing breaks while I sleep