external_api: fixed using deeplinks

This update opens links in the full body of the window so deeplinks will work on iOS Safari when using the external API in an iFrame.

react/features/deep-linking/components/DeepLinkingMobilePage.web.js

                         <button className = { downloadButtonClassName }>
                             { t(`${_TNS}.downloadApp`) }
                         </button>
+                        target = '_top'
                     </a>
                     <a
                         { ...onOpenLinkProperties }
                         {/* <button className = { `${_SNS}__button` }> */}
                         { t(`${_TNS}.openApp`) }
                         {/* </button> */}
+                        target = '_top'
                     </a>
                     { renderPromotionalFooter() }
                     <DialInSummary