[gui] adds listitem info label inprogress to determine if epg item is in progress

This adds a new listitem info label inprogress which indicates if the
associated epg tag points to a current ongoing program.
Added Container.IsUpdating
load navigation sounds from user config directory
jsonrpc: expose specialsortseason and specialsortepisode for episodes
[plugins] ensure we lookup the add-on as a plugin before trying any extension point when fetching a plugin:// directory
Merge pull request #4598 from jmarshallnz/plugins_run_as_plugins

[plugins] ensure we lookup the add-on as a plugin before trying any other extension point
Merge pull request #4590 from tamland/nav-sound-fix

Fix: navigation sounds from user config directory are never loaded
dvdplayer input stream: fix incorrectly set of EOF
paplayer: proper handling of non seekable streams
[musicdb] fix incorrect use of ComputeCRC, causing playcounts to not update. Thanks to amet
[cosmetic] get rid of unused variable
[musicdb] joins against album and song artist views should be LEFT, as some songs/albums have no artist. fixes #15149
[gui] don't show the 'remote path not found' message on directory failure unless it's a share. closes #15091, #15133.
[builtins] PlayMedia() should use a sort order appropriate for the items. fixes #15136
[PVR] bump add-ons
Merge pull request #4602 from opdenkamp/pvrgotham

[PVR] bump add-ons
FIX: [droid] crash when stat'ing /mnt/secure/asec on some devices (fixes #15148)
upnp: fix sort by upnp:rating
upnp: ignore "Unknown" as a single genre as it is added by Platinum
CDateTime: extend SetFromW3CDate() and add GetAsW3CDate(), GetAsW3CDateTime() and SetFromW3CDateTime()