Refactor KeyResolvers

This task is to do a minor refactor of the KeyResolvers:

• Remove the concept of setting a "global" resolver boolean. It looks like this isn't working anyway in the code. It's up to the resolvers whether they are thread safe or not (all of the default ones are).
• Remove unnecessary wrapping of KeyResolverSpi with KeyResolver objects
• Simplify KeyResolverSpi
• Remove KeyResolver methods to set properties on the resolvers.