Replace django-channels websocketbridge implementation

The following discussion from !1664 (merged) should be addressed:

• @Sporiff started a discussion: (+1 comment)

  @georgkrause @wvffle Just a thought: the websocketbridge provided by django-channels is no longer maintained. This is all we use from django-channels, and they are no longer supporting any Javascript implementation. Would it make sense for us to split this out rather than dragging in the whole dependency? This appears to be what others are doing and the advice being given in the forum.