Clean up stellar_file.h by removing obsolete declarations and includes
Add utility functions to interpret values in SSD as script expression

Sqcalci is for interpreting integer values.  Sqcalcb is for interpreting
boolean values.  Double values should be passed to sqcalcd, but it's
currently defined as CoordSys::sqcalc(), which should be moved to
stellar_file.h.
Make noise generated terrain's parameter customizable in SSDs

Ceres.ssd demonstrates this functionality.

In this process, intermediate structures for noise terrain are moved to
DrawTextureCubeEx's members.

Also, sfnoise3()'s returned value is normalized by maximum possible value
range, so we can expect the same terrainNoiseHeight parameter take similar
effect when terrainNoiseOctaves is changed.