Do not display background shape in fullscreen notification if there’s nothing in it

So nothing cover a photo when using AirPlay photo sharing
Improve AirPlay device visibility in iOS 7

For some reasons, my iPhone doesn’t always show mythtv as an AirPlay device, and more often than not only show it as an audio device.
After playing a lot with the various bonjour advertising data, what I can gather is:
- If AirPlay video reports a version >= 120.x; the iPhone will attempt to use FairPlay DRM no matter what RAOP reports (even if it reports no support for encryption)
- If there’s a mismatch of version between AirPlay video and RAOP: the iPhone 5 won’t show the video service
- If reporting a version < 110 in AirPlay video, then photo sharing doesn’t reliably work
- If bit 10 in features bitmask is cleared, it doesn’t reliably show up
So I set the AirPlay video version to 115.3 (made up value) that allows photo sharing, and RAOP also to 115.3 and it all seem to work nicely now
Revert "Have backendhousekeeper check for artwork update boolean."

This reverts commit f4669d6c1b752b943b2b2f04c7382445b88a3d70.
Add secondary check to prevent housekeeper task from running twice.

This adds an extra check to prevent a HouseKeeperTask from running
more than once simultaneously. This prevents an issue seen in a
misconfigured child task that was queued in concurrent passes. One
instance had not yet finished when the second one started a minute
later, and overwrote a shared pointer, eventually resulting in a
segmentation fault.

Cause spotted by Jonatan Lindblad.

Refs #11902
Add back ArtworkTask enable check... properly.

This adds the check for DailyArtworkUpdates back to ArtworkTask,
following its reversion in ca3a79bf407, but properly runs the
PeriodicHouseKeeperTask check so it does not requeue once per minute.

Refs #11902
Bump binary version.
Updated Spanish/Spain MythFrontend and MythMusic translation
from Antonio Marcos Lopez Alonso

Thank you Antonio!

Closes #11896

Signed-off-by: Nicolas Riendeau <nriendeau@mythtv.org>
Add missing toUTC() conversions in the preview generator.

Without these conversions, modification timestamps on
backend-generated preview files are reported in local time, but
interpreted by the frontend as UTC.  The frontend then converts this
to local time and uses that to set the modification timestamp of the
locally cached preview, effectively back-dating the cached file in
most time zones.  This messes up date comparison logic for determining
whether to regenerate or reload the preview image.
AlbumArt::cycleImage(): If we only have one image there is nothing to cycle