Live broadcasts: time in queue should show time left

[gbl08ma]

For broadcasts, it can be tricky to see for how much longer they will play (one needs to subtract their duration from the time at which they began playing, and the UI doesn't show the latter).

It should be possible to obtain this information on the client alone, but it requires combining the media consumption checkpoints with the queue data. It might be easier to change the API so that this information (i.e. when the current entry started playing) is sent as part of the queue data.