Embedded xBlock sharing (#46)

[satyarapelly]

• Fix, rename language code and change style

• Keep current video and captions state

• Upgrade player

• Update documentation

• Extract transcripts code base to separate plugin - 1:1 mostly

• Clean player initialization module

• Update requirements

• Update player template

• Add separate transcripts plugin

• Add css transcriptsAmpPlugin

• Add css transcriptsAmpPlugin

• Update Transcripts Plugin

• Enforce lists styling in Transcripts Plugin

• Add video download via AMP native Download Dashboard

• Add new xBlock field for assets download switch

• Add Player assets download modes

• Fix quality checks

• Fix unit tests

• Take back footer download buttons

• Make footer buttons to honor transcripts-enabled flag

• Add share player

• Rename None in Off

• Fix style

• Update documentation

• Fix poster and transcripts overlapping

• Remove share button on embedded player page.

What does this PR do? Please provide some context

Where should the reviewer start?

How can this be manually tested? (brief repro steps and corpnet-URL with change)

What are the relevant TFS items? (list id numbers)

Definition of done:

• [ ] Title of the pull request is clear and informative
• [ ] Add pull request hyperlink to relevant TFS items
• [ ] For large or complex change: schedule an in-person review session
• [ ] This change has appropriate test coverage
• [ ] Get at least two approvals

Reminders DURING merge

1. If you're merging from a short-term (feature) branch into a long-term branch (like dev, release, or master) then "Squash and merge" to keep our history clean.
2. If merging from two longterm branches (like cherry picks from upstream, dev to release, etc) then "Create merge commit" to preserve individual commits.

[satyarapelly]

I will create new