Missing audio alert needs to be shown in navigation

[BenjaminScholtens]

We need to show that audio is missing at all levels of the navigation. We can simple swap the audio icon/dot as as a red alert icon at each level. We already do this for the cell. We just need to show it in the chapter navigation, page navigation, and the file progress.

NOTE: Before we launch this feature we need to restore missing audio that our sync is dropping for some reason. See work in Gan-Nanchang.

We should use this feature locally to view our live project and identify missing audio. We should see if we can restore the audio before we deploy this feature.
look at #656