Refactor exceptions raised during EWS message passing.
Set children in right order

The XML elements need to be in the right order for a CreateItem
request to work properly. Fix it.
Minor typo in folder.py
Make Field.to_xml() more generic
Add ability for creating contacts on server
Improved exception messaging for EWS errors

This is still not enough. Every request has a specific response
format that will give more detaile information about what exactly
went wrong. For now we are only extracting some common errors.