Update old transcripts metadata present in video xml with the new transcripts for backward compatibility.

added unit tests

updated edx-ace version

fixed quality violations

Fixed quality violations

Changed ACEMessageType to BaseMessageType

Use backoff when calling Sailthru API to retry upon optout timeouts.

Bumps xblock-utils to v1.1.1
Bumps xblock-drag-and-drop-v2 to v2.1.6

React code (in jsx files) was not being extracted at all. Fixed this
by updating to edx-i18n-tools 0.4.5.

Also, template literals (feature of es2015) don't work well with
gettext at all. So convert those instances to HtmlUtils or
StringUtils interpolation calls.

FEDX-505

This reverts commit a7fa0c21.