Play queue time indicator improvements

Description

These ideas come from https://forum.videolan.org/viewtopic.php?f=35&t=155998&sid=c91b0d3e5560b6ff1f5919095f9ad557#p513183

1. Display the time in sec instead of min
2. Hide it when there is only one track in the queue
3. Add a mode saying at what time the queue will be finished

App mode

Smartphone

changed milestone to %3.3.x

added feature label

changed milestone to %3.4.x

mentioned in issue #1634 (closed)

closed with commit f14dfa14

closed with commit 02bc476e