frontend: move WebRTC server address to Settings/Video

[ES-Alexander]

Current behaviour

We have video connection settings in both Settings/General and Settings/Video, which is unintuitive, and may mean users don't realise one or the other section is available, or what the differences are between them.

There are also individual windows for video player widget configuration, video recorder mini-widget configuration, and the video recordings library, so there are lots of video-related interfaces to know about and keep track of (but the widget-specific ones are at least semantically for different purposes).

Expected or desired behaviour

1. We have a Video configuration page, and it seems intuitive that the WebRTC signalling configuration could be moved there from the General page
2. That configuration does still seem quite high level, and existing users may be familiar with it, so we may wish to include a link to the Video page on the Settings page to make it clear that's where to go for all general Video streams/connection configuration

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.