Trait Array of positive integers/floats does not work

[martinRenou]

In openfoam_model.py, the channel size is an array of positive floats.

#: The channel size.
channel_size = Array(PositiveFloat, (3,), [1.0e-1, 1.0e-2, 2.0e-3])

But TraitError is not raised when trying to give an array containing negative floats.

We could fix the error with three PositiveFloat traits (channel_size_x, channel_size_y, channel_size_z)

[martinRenou]

Or we could create a custom PositiveArray trait in local_traits.py

[martinRenou]

Fixed