Investigate promise failure on Safari

[ApolloLV]

I think I remember some failures of the JS client on Safari, let's take a look at the issue.

[ApolloLV]

From https://webkit.org/blog/6784/new-video-policies-for-ios

[ApolloLV]

We should consequently detect safari browsers and serve their videos muted

[ApolloLV]

See also https://stackoverflow.com/questions/20347352/html5-video-tag-not-working-in-safari-iphone-and-ipad for other weird stuff Safari is doing with videos and how to circumvent them.