Planned skinning changes for Kodi v18

i know it’s a bit early since we’re still wrapping up v17 for release, but there are a few changes for the next version that are worth mentioning…

1. we’re going to drop the now, next & channel listings (id 11, 12, 13) from the PVR Guide window.
see: https://github.com/xbmc/xbmc/pull/10503

2. we’re dropping support for using a hyphen as a none value
see: https://github.com/xbmc/xbmc/pull/10389
and: https://github.com/xbmc/xbmc/pull/10388

all these changes are safe for v17 as well, so if you’re that way inclined you can start by removing them now.