Make Entity subclass of dict

[huguesv]

We should integrate this change:
Azure/azure-sdk-for-python#411

We already allow passing dicts or Entity objects into azure storage, but for queries, we always return Entity objects. This change lets the user access the entity objects as dicts.

[huguesv]

Note that we can get rid of the WindowsAzureData base class, and just derive from dict.
In serialization code, we can remove the check if it's a dict or an entity object, since they are all dicts.

[jehine-MSFT]

Hello @Philmist,

@emgerner-msft merged the suggested fix. A build with this fix will go out with the next major release.

Thanks for the feedback!

[jehine-MSFT]

Hello @Philmist,

We have released the 0.30 version (#132) which addressed this feature request. If you have issues with the new version in regards to this issue, please reopen it and continue the discussion.

Thanks!