Add support for IncludeMimeContent Flag in GetItem calls to retrieve the full mime content of emails by specifying this flag
Fix for https://github.com/zenchild/Viewpoint/issues/84

The input format for extended_properties via extended_field_uri is possible in a few variations see http://msdn.microsoft.com/en-us/library/exchange/aa564843%28v=exchg.150%29.aspx

The current implementation does not work <at all>.

This commit adds support for extended_property requests via PropertyName, while definitely incomplete it is the step into the direction to be taken.
* improve upon the previous commit, don't use an array but an hash to expose the extended properties of an email,
  the extended properties are known (they have to be specifically requested in the first place)
  and it makes more sense to retrieve the values by item.extended_properties[:PropertyName.downcase.to_sym]
Merge pull request #81 from TobiG77/master

Add support for the IncludeMimeContent Flag in GetItem calls