ActivityStrea.ms Cleanup

Update the classes for activity streams objects to encapsulate json
elements so that parsed properties are not affected.
Fix duplicate follow bug

Following the same entity twice caused duplicate edges to be created,
making later reads fail.
Add DELETE for stream entry resource
Add following resource

Add a resource to the API to allow retrieval of the entities a user
follows.
Added followers resource

Add a resource to the API to allow retrieval of the users following an
entity.
Prep for 0.4.0 release
Add local graphml xsd

Add the schema validation file to the project so that tests do not need
to hit an external network resource.
Output graph export exceptions