Helper method to convert str->int in all bases
New Mixin for readonly properties

Certain fields are only created when the data is received from the
server; they are never written back to the server. E.g.
LastModificationTime. This new Mixin will ensure that a field
is not written to the XML representation of an Item.
Gender type and misc. EWS data type changes
Better support for ExtendedProperties

- moved ExtendedProperty from contact to item
- Ability to identify tagged properties in the input and have
  an easy way to access them
- Gender and LastModifiedTime extended properites are now
  working based on the new framework
Update test for contact with gender prop