Another attempt to fix #1041. This time I'm sending real data from decoder
once after playback started.
#1041 in progress: decode first sample batch right in OpenAL_SoundStream::play()
Merge remote-tracking branch 'corristo/osx-music-fix'
FindSDL.cmake is unused
Moved includes to appropriate place
Get rid of useless return values
Closes #888: Treat "Bip 01" as animation root if existing
Terrain: change world bounds from AABB to 4 floats
Don't list unnamed quests in the quest book
Fix AiCombat for creatures with weapons
Terrain: support alternate coordinate systems. Get rid of LoadingListener for now
Terrain: remove hard dependency on shiny - can now be compiled without it (fixed function)
Render maps after *all* cells have finished loading

Still not fixing Bug #772, but at least this will allow for background loading of terrain.
Terrain: fix an embarrassing copy&paste mistake.
Terrain: moved ESM::Land load to earlier in the startup procedure

Required for background loading as we cannot load ESM::Land data from background threads.
Terrain: take cell world size into account for LOD selection
Terrain: geometry is now loaded in background threads.

TODO: background load layer textures and blendmaps.
"Distant land" setting has been removed for now (i.e. always enabled).