Add human-readable cron descriptor

[mxdvl]

amigo/app/views/showRecipe.scala.html

Line 61 in c4fd080

<p>Build schedule: <code>@recipe.bakeSchedule.map(_.quartzCronExpression).getOrElse("(none)")</code></p>

It would be handy to get a human-readable description next to the cron jobs, to prevent users from having to click away.

The cron-expression-descriptor package seems to exist in many languages, including JavaScript if we want to to this client-side only.