As posts are always delivered also to reshare root, comments should also be delivered to reshare root, for concistency.

* add a class for checking pod connectivity
* extend pod model to handle new functionality
* add an admin frontend to list pods and re-trigger checks manually
* add a daily worker to run through all the pods
* add unit tests for most of the new code

closes #6310

closes #6223

refactoring:
- remove unused return-values (were used for caching, which was removed again)
- remove transaction (doesn't help here, added in 26151263)

closes #6068

Fixes #6067

closes #6022

closes #6009

closes #5991

Since the Facebook API has changed and additional permissions are required for all users on a pod to cross-post, an additional 'authorized' flag is needed to be set for the Facebook service.
This flag allows either all users, one user or no users to use the cross-posting service.

Clarifies the situation for #5923, #5260 and #5085.

closes #5985

closes #5960

closes #5962

closes #5958

Fix the IE version number extractor to work without space between MSIE and the version number, close #5858

Strip markdown from the heading of a post. Impact notifications, email subjects, SPV <title>, the Atom feed...

Conversation recipient validated

- Conversation foreign recipient not required to be validated.
- Added 'peter' as spec_helper user.
- New fixture, new statistic values.

- Clearer identifier names

opengraph_parser is basically unmainted, issues are ignored
or deliberately closed without fixing. It pollutes the global
namespace and has no verification of correctness.

The opengraph gem has basically the same issues, not really maintained,
unreleased patches on master since over a year, not really smart either.

So I created my own version and while at it, why not strive try to be
complete and robust, although it's still a work in progress.

This also improves general URL detection by parsing them
from the message after stripping markdown.

An additional dependency was added to support
fetching sites that require cookies to work at all.
For the same reason Faraday's default redirect limit was
bumped.

... and a stealth-commit of an already introduced bug prevention system.
;)

Conflicts:
	spec/helpers/notifier_helper_spec.rb

That's at least readable, return false just causes
silly follow up errors