Transcript auto-scroll, analytics date ranges, and GitHub embeds

Following along with a video's transcript is now easier than ever. While playing any video you can click the auto-scroll icon to have the page keep the transcript visible and in sync with the video.

Other feature updates and improvements

• We no longer send email notifications to disabled members
• Users are now notified when they are @-mentioned in a video's description
• Fixed several z-index issues that were causing visual issues throughout the application
• Videos analytics can now be shown based on a date range
• Comments can now be removed from a video's transcript
• Notifications can now be sent to private Slack channels
• Fixed a bug where users were unable to import from a shared Google Drive