Add new ellipsoid terrain height class.

This class creates an ellipsoid surface representing equatorial bulges
for rotating bodies by returning the height value between a point on a
sphere of Polar radius and a point on the ellipsoid surface in the
center to Polar radius line (using the aspect ratio which gives
Equatorial to Polar radius).
allow CustomBody to control SystemBody aspect ratio
Show radius and equatorial bulge ratio for stars in system-info-view

New translatable string EQUATORIAL_RADIUS_TO_POLAR_RADIUS_RATIO.
Enable ellipsoid surfaces for all stars.
Create aspect ratio between 1.0 and 1.8 for stars of type O, A, B, F in sysgen.
adjust radius and maxfeatureheight for ellipsoidal bodies
clamp TerrainHeightEllipsoid result to be >= 0.0

This is just because rounding errors can push it very slightly negative
and trigger the negative-height assertion.
make Achernar a ful custom system, with star aspect ratio 1.56
Added missing Elipsoid terrain type file to VS2010 and VS2012 terrain projects.
Merge pull request #2178 from johnbartholomew/fat-stars

Fat stars
Updated changelog.txt