Store and retrieve related items from RelatedItem attribute (complete refactor for new project)

[petero-dk]

fyi I tried placing the logic a couple of different places and this seemed to be the smartest. What do you think?

[petero-dk]

@dei79 sorry for the long digestion period. I have been completely away from my projects using this library for this time and I finally had some time to update them, and by extension, my PR to this project.

I hope the RelatedTable attribute is still relevant. I tried to create it as an extension using Virtual Attributes, but they do not have enough low level access so I could not find a way without extending the Interface for VirtualAttributes, and trying to make it backwards compatible I resorted to Abstract classes. The reason I mention it here is if you think I should do that instead.

Let me know if you are still interested in this addition.

[petero-dk]

Also I have managed to get the tests to work locally. I will make some tests for the new attribute. I cannot get the tests to work on Github, it looks like it does not load the credentials for the remote Table storage when the Author is external to the project.

[petero-dk]

Replaced by #23 since I accidentally merged multiple tings into the same branch in order to create a demo release