RTP packaging/bundling support

[fdelapena]

As RTP replacement (aka OpenRTP) evolves, bundling RTP assets in some platforms need some work bundling them (e.g. Android and video game consoles), paths setup and such.

How should it be bundled on Windows and macOS? on *nix sounds the usual as a package and marked as player/editor dependency. Determine official package paths and prevent conflicting with overriding paths (if somebody wants to force official RTPs or for testing purposes).