Minor updates to Resource and ResourceService.

Refactoring agent and user account binders. Generalized UserAccount holder to Agent.
Adding connections to UserAccount. Added appropariate routes.
Added support for patching existing resources.
Adding messages: create message and retrieve by id.
Resource UUID generation fixed.
Added handler for deleting a message.
Added support for SPARQL queries.
Setting the global context for Jena TDB to use the default graph as the union of all named graphs.
Added handler for retrieving a list of  messages received by a user.
Added a first working draft for the ThingsNet spec.
Removed static identification of a user's messages.
Added sample requests to README.
Refactoring of RDF resource models.
Retrieving the messages received by a given user now returns graphs (instead of a result set).
Basic validation of HTTP request parameters. Added proper HTTP responses.
Updated STN spec and made it available as public asset.
Added platofrm spec parsing for demo client.
Updated STN spec.
Added mywebid parameter as placeholder for authenticated requests.
Merge branch 'dev' into demo-client