Use correct numeric format based on selected locale (Qt domain part)

This changes the numeric format of many values printed to the UI to
reflect the correct numeric format of the selected locale:
- dot or comma as decimal separator
- comma or dot as thousands separator

In the Qt domain the `L` flag is used case specific mostly
in qthelper.cpp.
Then the helper functions get_xxx_string() are used more consistently.

Signed-off-by: Stefan Fuchs <sfuchs@gmx.de>

profile-widget/divecartesianaxis.cpp

@@ -271,7 +271,7 @@ void DiveCartesianAxis::animateChangeLine(const QLineF &newLine)
 
 QString DiveCartesianAxis::textForValue(double value)
 {
-	return QString::number(value);
+	return QString("%L1").arg(value, 0, 'g', 4);
 }
 
 void DiveCartesianAxis::setTickSize(qreal size)