* Get participant specific video element

We now have the ability to select the video element for specific participants. I'm tweaking the jitsi-meet-electron app for my use case. I need to open Always On Top windows for specific participants, so the current _getLargeVideo() wont suffice.

I made a post about this in the Developers section on the Jitsi Community Forum, but it got blocked by Akismet.

* Add dots at end of sentence.

* Fixed ESlint errors and add additional check for iframe.

* Use _myUserID instead of string.

* Return the local video by default if participantId is undefined.

* Fixed mistake in string template.