[Bf-python] Mesh custom layer api change

[Campbell Barton]

Hi, currently python can add custom data layers to a mesh, (added by Briggs)

One part of the API Id like to change is how you select a layer type.

mesh.addPropertyLayer(Mesh.PropertyTypes.FLOAT)
mesh.addPropertyLayer(Mesh.PropertyTypes.INT)
mesh.addPropertyLayer(Mesh.PropertyTypes.STRING)

Would it be ok to change this to use python types?

mesh.addPropertyLayer(float)
mesh.addPropertyLayer(int)
mesh.addPropertyLayer(str)

- Cam