Human readable format for cron in the UI (scheduled builds)

When making a POST call to the scheduled builds API, you have to use cron format:

#!python

0 0 5 ? * MON-FRI *

Since this API directly hits the cron service, customers won't be able to see if this worked until the scheduled build fires. We should create a human readable format upon POST'ing to the UI to make it easier to verify scheduled builds.