* Add AuthorizeDatabase API to QueryAuthorizer to verify a user has
appropriate access to the specified database
* Update serverFluxQuery handler to require a meta.User when auth is
enabled
* update Flux createFromSource and createBucketsSource dependencies to
require Authorizer when auth is enabled in configuration
* update createFromSource to verify read permissions for each bucket
specified in a Flux query
* update BucketsDecoder, which implements the buckets() Flux function,
to return buckets that the user has read or write permissions to
* add unit tests to verify authentication is required for Flux HTTP
requests when auth is enabled in configuration
Stuart Carnie