Adds participant connection status notifications

When we receive a conference failed event with reason not allowed we show that page.

Feedback window improvements.

Pin hover improvements

Default cursor for icons

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.

We used to rely on 'currentTime' of the video element, but we execute
'updateView' from the 'onplay' callback and on fast machines it may
happen that the value is 0 even though the video has just started.

At any point of time we display one of the three: video, avatar or
blackness. The purpose of this commit is to make that fact more clear
in the code.

The video or the avatar on a thumbnail will be displayed in greyscale
when the user is having connectivity issues.