QScreen manual test improvements: fields resize, better formatting

QScreen manual test improvements: fields resize, better formatting

It's necessary to set the fieldGrowthPolicy on the QFormLayout in order
to have expanding fields on the Mac.  Geometry formatting with
negative x and y values looks better.  Display fewer
decimal digits for double fields.

Change-Id: Icb252c0c3fb7b605253e04c3361beba124570840
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>