Change WDK guest user creation mechanism

WDK has a Jersey filter that ensures there is always a user present for service request methods to use. If no registered user is logged in, this serves as a persistent guest user (attached to the session). Since the conversion to a client/service architecture, this method of providing users is overkill since not all services (in fact, many services) require a user or are user-agnostic (i.e. could use the "system user".

We should rework WDK to work more like our new service architecture, letting specific endpoints declare whether they need a user or not. This issue is to track ideas around this concept and may be related to the goal of factoring user authentication into a bearer token model, where WDK would simply be one of many services that respect VEuPathDB bearer tokens. It may even be a contributing reason to move WDK to the new service framework.

No files, tests, or entry points are named. Start by locating the Jersey filter that creates the persistent guest user and compare it with the newer service architecture. The issue needs an agreed design for endpoint-specific user requirements and the possible bearer-token model before implementation can be considered done.