Wakeup the backend to run mythfilldatabase

This uses MythFillSuggestedRunTime, for xmltv sources (+24 hours), for
datadirect whatever time was suggested by TMS to ensure that we always
wake up the backend to collect guide data (xmltv, DD only, EIT is not
yet supported). Using MythFillSuggestedRunTime is a bit of a hack, but
it's already set for Schedules Direct so this was the simplest
solution.

For now the "Run guide data program at time suggested by the grabber"
setting MUST be enabled for this to work as intended.

Without this fix the backend won't wake up to grab guide data from
xmltv/SD sources and that may result in it eventually running out of data
entirely.