Additionally, this restores previous background / text color for media spoiler.

* Custom emoji

- In OStatus: `<link rel="emoji" name="coolcat" href="http://..." />`
- In ActivityPub: `{ type: "Emoji", name: ":coolcat:", href: "http://..." }`
- In REST API: Status object includes `emojis` array (`shortcode`, `url`)
- Domain blocks with reject media stop emojis
- Emoji file up to 50KB
- Web UI handles custom emojis
- Static pages render custom emojis as `<img />` tags

Side effects:

- Undo #4500 optimization, as I needed to modify it to restore
  shortcode handling in emojify()
- Formatter#plaintext should now make sure stripped out line-breaks
  and paragraphs are replaced with newlines

* Fix emoji at the start not being converted

* Redesign video player

* Use new video player on static public pages too

* Use media gallery component on static public pages too

* Pause video when hiding it

* Full-screen sizing on WebKit

* Add aria labels to video player buttons

* Display link card on public status page

* Fix fullscreen from modal sizing issue

* Remove contain: strict property to fix fullscreen from columns

- Use plaintext
- Strip out URLs
- Strip out mentions
- Strip out hashtags
- Strip out whitespace from "overall" count
- Consistent between JS and Ruby

* selectively Revert "Fix regressions from #2683 (#2970)"

This reverts commit 72698bc3b4.

* Revert "Handle hashtags in spoiler_texts (partial fix for #699) (#2683)"

This reverts commit e2491680e6.

* Fix regressions from #2683

Properly format spoiler text HTML, while keeping old logic for blankness intact
Process hashtags and mentions in spoiler text
Format spoiler text for Atom
Change "show more" toggle into a button instead of anchor
Fix style regression on dropdowns for detailed statuses

* Fix lint issue

* Convert spoiler text to plaintext in desktop notifications

* services: scan spoiler_text for hashtags (#699)

* views: link hashtags from spoiler_texts

This covers linking hashtags from within the spoiler
text on the server-generated pages.

* services: fix string concat going into hashtag RE

Cleaner Ruby syntax, may handle immutable strings better

* add haml_lint to Gemfile

* add .haml-lint.yml

* fix warnings of haml_lint

* Add html lang attributes around statuses

* Remove urls from language detection

For the 'time ago' value of stream entry simple statuses and the timestamp value
of detailed statuses - output their UTC value and use the browser timezone to
convert locally.

* 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

* Remove trailing whitespace

* Use query methods instead of explicit .blank? checks

* Add coverage for embedded status view

* Refactor embed view to eliminate @external_links variable

before. In the API, attachments now can be either image, video or gifv. Gifv
is to be treated like images in terms of behaviour, but are videos by file
type.

Federate spoiler_text using warning attribute on <content /> instead of a <category term="spoiler" />
Clean up schema file from accidental development migrations

h-feed, h-card and h-entry

fix #361 with rich OEmbed display via iframe, fix #237 by hiding sensitive
content behind a spoiler on public pages