MythImage: fix loading images from slave BE's

52fa7ecc added a check in MythImage::Load() to make sure the file exists but
unfortunately RemoteFile::Exists() only looks on the master BE so trying to
load an image on a slave would always fail.

Just do a quick fix using RemoteFile::FindFile() for now. The proper fix would
be to fix RemoteFile::Exists() but that would require more intensive testing
to make sure fixing it doesn't have some unexpected side-affects.
fix -Wstring-plus-int from clang
make parameter names consistently lowercase

Since [3d9155909f] the parameter names used inconsistent upper and lower case.

There are two places in libmythupnp where the incoming packets are decoded, in
one place they are converted to lowercase, in the other place they are not.
This commit had made it lowercase in both places but did not change the code
that accessed the data, the caused serious discombobulation and the end of UPNP
watching through out the world.

Patch by Steve Beinicke

Fixes #12006
Services: Add a GetFormatDateTime endpoint, this just covers all the different variations offered by the internal toString() method and reduces code duplication in the WebFrontend.
WebFrontend: Add a Recording Rules page.

It's unfinished and the layout/content will probably change in the
final version once I've solicited some feedback on what people
actually want from it.

Refs #11938
Services: Expose missing Content endpoints to the Scripting interface
Remove jquery load from hlstest.qsp, it already loaded and loading it twice causes breakage.
AlbumArtImages: load the hostname from the database
MythMusic: switch the filescanner to scan the 'Music' storage group
Merge remote-tracking branch 'upstream/master'