CornerpointChopper::writeGrdecl(): Write fewer items per line

This is in preparation of increasing the vector output precision to
reduce the impact of rounding errors in subsequent upscaling.  The
change impacts floating-point vectors only.

Background: The ECL simulator stipulates an upper bound on the
number of characters in a record (i.e., one line) and while we don't
have such limits, there's no reason to emit lines that can't be
input by other tools.
CornerpointChopper::writeGrdecl(): Increase vector precision

This commit increases the precision of the (floating-point) vector
output (e.g., permeabilities) from method writeGrdecl().  This
reduces the impact of rounding errors when the sub-set sample is
output to disk for subsequent processing (e.g., property upscaling).
Merge pull request #632 from bska/cpchop-precision

Increase precision from CornerpointChopper::writeGrdecl