Create a decorator class for python designs

[azimov]

At the moment names, descriptions and parents are loaded by modifying the function obects directly.
A decorator design pattern along the lines of

@gsmodutils.utils.design_function(name="...", description="..", ...)
def gsmdesign_name(model, log):
   ....
   return model`

This approach could also allow designs to be picked up by gsmodutils in a more sophisticated manner than simply adding them by the function prototype prefix (gsmdesign")

[azimov]

Completed with gsmodutils.utils.design_annotation decorator. Will be included in next release.