ctkDoubleSpinBox now keeps original precision until edited

QDoubleSpinBox rounds the input value with a given decimals number.
This can loose important precision. Here we apply the same mechanism as
for ctkDoubleSlider: store the original value with full precision.

http://www.na-mic.org/Bug/view.php?id=3261
Add ctkDoubleSpinBox::SizeHintPolicy

Sometimes we don't want to bound a spinbox with a min and max.
If the minimum and maximum of the spinbox where very large, it would
enforce a wide spinbox.
With SizeHintByValue, the spinbox takes only the space it needs.

ctkCoordinatesWidget is no longer bounded by default.