Refactor animationcurve loader, add some more sun params

@pingopete, take note! :)
You can add a sunBrightnessCurve {} node to REALSOLARSYSTEMSETTINGS with
a series of keys, and sunAU = foo for the new AU scalar.
The originals are (time, value, in, out, mode):
**DUMP** Sun AU: 13599840256
Key -0.01573471, 0.217353, 1.706627,1.706627 : mode 0
Key 5.084181, 3.997075, -0.001802375,-0.001802375 : mode 0
Key 38.56295, 1.82142, 0.0001713,0.0001713 : mode 0
so you can do
sunBrightnessCurve
{
key = 0 100000 0 0
key 153000000 1 0 0
etc
}
}