Add support for ApprovalStore in @EnableAuthorizationServer

If user defines a @Bean of type ApprovalStore the AuthorizationEndpoint and
WhitelabelApprovalEndpoint change their behaviour accordingly.
Remove bundlor plugin
Refine ApprovalStore configuration a bit

Rather than always create a @Bean of type TokenStore we now look for
beans *named* "tokenStore" and "approvalStore" and back out if one
of those already exists. That makes more sense for stateless token
services (like JwtTokenServices).