FMod - Song format flexibility

Today I rearchitected the GalaxyAudio class in FleexCore2 (which represents a Keen Galaxy audio archive) to lazily parse the different kinds of sounds only when requested. If a parsed sound is requested, the stream of bytes is parsed and the sound is stored in a cache. Other components can request raw chunks, which serialize the sounds back to bytes if they've been parsed or just return the original byte stream if not. Abiathar now avoids triggering the parsing of IMF songs unless needed to turn a headerless IMF into a chunk. This allows preserving audio entries of arbitrary format in IMF chunks.

Since FleexCore2 changed, the ImfPreview extension had to be updated as well. While I was working on that I also made ImfPreview use Abiathar's standard "one moment" dialog instead of its own copy.