Display summary of attachments in description, and mark up content
warning if present, e.g.:

    Attached: 3 images · Content warning: Dota 2

When text is not supposed to be hidden, it looks more like:

    Attached: 3 images

    Here is the text of the toot

With #6817, multilinguagility should be assured...

- Return all images as og:image
- Return videos as og:image (preview) and og:video
- Return profile:username on profiles

* add og:url to stream_item view

* add og:url and text to about/show

* add og:url to profile, followers and follows pages

* Move site title helper to instance helper (name change only)

* Remove newline in <title> tag

* Add site_hostname helper method to wrap up local_domain value

* Use site_hostname helper in places that need local_domain value

* Add option to disable verify partial doubles

* Add show_landing_strip? helper method

* Use show_landing_strip? helper in accounts and stream entries views

* Fix naming in view specs

An attempt to open a brand new Mastodon instance configured
as SINGLE_USER_MODE=true will cause an exception.

Enable temporary registration if we have no users in the database

Fixes #1817

* significant improvement in microformats markup

This is a huge improvement and I believe will close #965.

Had these microformats reviewed by others in the community to help
ensure they are at least correct, if not complete.

I did not want to change the structure of the page, and so there it does
not fully mark up the entire ancestry chain, or reply chain, only the
direct decendants and direct ancestors are correctly associated, but
this is likely fine as the most important bit is to have access to the
urls for those toots which are now correctly fetchable.

* improve code climate

* trying to pass code climate tests

* code climate

* fix p-summary for content warning posts

* fix error introduced when merging via github

* Add helper method to return Setting.site_title

* Use site_title helper in application layout

* Use site_title value for og:site_name

for avatars/headers, resize avatars down to 120x120 instead of 300x300. Set cache headers on S3 stuff, also
make it private (aka only accessible via expiring links to prevent hotlinking)