Merge remote-tracking branch 'refs/remotes/origin/oppia-1647-multiple-audios' into release-7-4-9

Merge pull request #1359 from jjoseba/oppia-1647-multiple-audios

Merge remote-tracking branch 'refs/remotes/origin/oppia-1664-update-webview-scroll-condition' into release-7-4-9

Merge pull request #1358 from AlbertoMoreta/oppia-1664-update-webview-scroll-condition

Merge remote-tracking branch 'refs/remotes/origin/oppia-1666-privacy-policy' into release-7-4-9

Merge pull request #1356 from jbc25/oppia-1666-privacy-policy

Merge pull request #1357 from AlbertoMoreta/oppia-1643-improve-points-consistency

OPPIA-1647: Update JSInterface to take into account multiple audios

OPPIA-1664 - Add JSInterface to modify WebView scroll condition inside a PageWidget

oppia-1666 - added privacy policy checkbox

OPPIA-1643 - Add extra condition if tracker uuid is null

Merge remote-tracking branch 'refs/remotes/origin/oppia-1667-fix-horizontal-scroll' into release-7-4-9

Merge pull request #1355 from jbc25/oppia-1667-fix-horizontal-scroll

Merge pull request #1354 from jbc25/oppia-1610-upgrade-gradle-and-libraries

oppia-1667 - Added extended classes to fix this problem (https://stackoverflow.com/a/9925980/1365440)