feature: added wrapper.picklist property  - a dynamic picklist object
feature: added wrapper.picklist property  - a dynamic picklist object

also added wrapper.refresh_picklist method which simply replaces the
picklist object with a new one.

allows for instant resolution of picklists with no extra setup. eg:
ticket.priority = at.picklist['Ticket']['Priority']['Critical']
will set the ticket.priority property to the corresponding id from the
picklist
MattParr/python-atws