rebrand cmake buildsystem for binary addons

This PR has the same goal as #5538 but it contains additional logic to maintain backwards compatibility to addons still using the `xbmc` dependency and include paths instead of the `kodi` dependency and include paths.

The first commit basically changes everything from `kodi` to `xbmc` but keeps some backwards compatibility files which will print a deprecation message.
The second commit fixes an issue that is also present in current master. The APP_NAME variable set in xbmc/kodi-config.cmake is currently empty but should say `Kodi`.
The third commit renames the `XBMCROOT` variable used by the cmake buildsystem to `APP_ROOT` but also keeps backwards compatibility so `XBMCROOT` can still be used (and is still used on linux, android etc).

I've tested this on win32 with the original audioencoder addons and the ones that @notspiff has kindly rebranded for us and all worked fine with the only difference being that our original audioencoder addons show a deprecation warning during the build.