[FT] ship design worksheet

If you have the FTFB ship design Excel worksheet, you may want to change the
cell that calculates the mass cost of FTL to:

 =IF(B14=0,0, MAX(1, ROUND(0.1*B9,0)))

I've added the MAX function because otherwise a small ship can have FTL for
zero mass due to rounding. (Note: I've also done some other stuff to it so I
don't guarantee the cell references above will be correct. B9 is ship's mass;
B14 is the input field for FTL drive).