Ability to define the service id for Raven client

Instead of generating a service id with a big ugly sha1 inside (like `monolog.raven.client.4b9d0f59c45d393c0fc2ac65d6f07ff1b71954cd`) to define the Raven client service, we can define a custom service id.
Rename service configuration for Raven

Also update the xsd to add Raven config options
Merge pull request #79 from j0k3r/raven-service

Ability to define the service id for Raven client