Uses some ES6 syntax. Also removes inputHeight key for resolution as it makes no sence to have dictionary with one key. Removes some code duplication. Makes code consistent: method params for updateLocalStats and updateRemoteStats.

Enable ESLint on jitsi-meet with the same configuration and the same
goals as in lib-jitsi-meet.

Destroy is just hiding current tooltip, we also need to remove other attributes to stop showing the tooltip.

When user reconnected and the avatar is displayed we need to perform
full large video update in order to transition correctly.

Renames 'videoConnectionMessage' to 'localConnectionMessage', because
it is displayed when we're having problems with our local connection
and a different one will be shown for the remote connectivity issues.

Grey filter will be applied to the remote video/avatar displayed on
"large" and a message indicating remote connectivity issues will be
shown on top of that.

The 'wasVideoRendered' flag will tell whether or not we have any video
image rendered(even if stalled) on the large video element.

When the user is having connectivity issues we use the image cached in
the video element to show the preview in greyscale. It looks like this
cached image gets invalided after prolonged periods of time the video
element being hidden(and it is hidden when the video is muted). So we
never show this image if the user gets muted during connectivity
disruption in order to avoid blackness.