[Registry-dev] Adding more tags related features to the registry

[Chathura C. Ekanayake]

Currently we are having only two tags related searches in the registry. 
Those are to get the resource paths tagged with a given tag
and to get the tags for a given resource path.

But I think there are many other tags related searches / features that 
would be nice to include. Below are some of them:

1) Get current user's tags on a given resource
2) Get all the tags applied by the current user
3) Get all the tags used in the registry (sorted by the popularity)
4) Get the list of resources tagged with a given tag by the current user
5) Given a resource, get the list of resources related by tags

I think we should add methods to support above tags related features to 
the Registry interface. As we support tags as a primary concept, we 
should add rich functionality to support tag related searches.

Thanks,
Chathura