ISIS-367: removing DeploymentType.CLIENT

... since we no longer support this mode (client/server remoting removed a while back).
ISIS-367: removing IsisContextForWicket since no longer used....

... and removing thread counting from AuthenticatedWebSessionForIsis.
ISIS-367: EventMetadata provides id; commented out entries for github pub service in example

* EventMetadata#getGuid renamed to EventMetadata#getTransactionId
* EventMetadata#getSequence added
* EventMetadata#getId added
* added commented out entries for example configuration of using github-hosted pubsub service for ActiveMQ/RA.