orientation features in 2D have different ranges

[dlegland]

For 2D regions, three plugins provide measure of orientation, but the range is not the same for the three:

• EquivalentEllipse yields values between -90 and +90
• OrientedBox yields values between 0 and +180
• MinFeretDiameter yields values between 0 and +180

It would be nice to consider only one range.