Change WDK guest user creation mechanism

[ryanrdoherty]

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.