v5.1.6 - Add guidance to video when subtitles are not available

Show guidance when subtitles aren't available (#140)

* add state to identify if video was started via autoplay

* render guidance component on placeholder

* style guidance banner

* rejig things to handle video reloading on homepage

* convert guidance to a class

* style close button

* WIP tests

* hover state on close button

* close banner after 5 seconds

* wrap guidance in mixin

* hide banner when it auto closes
this way screen readers can still access it

* add tests for guidance

* link stright to video transcripts section

* tidying

* linting

* use font smoothing to match the placeholder

* remove need for o-buttons

* clear timeout if banner removed early

- prevents banner disappearing early when a skipped to the next video
in a playlist before the previous banenr was hidden

* implement listen once

- `once` option not suppported by IE 11