Correct signatures of Aggregator methods for type safety

[dvgica]

Previously, the authData passed to the various user-facing GenericAggregator methods was useless - it was a non-specific type. This PR tweaks varies types and signatures to allow it to be specific. Now, implementors of the Aggregator class specify which AuthData type they expect to handle. If an Aggregator handling an incorrect type of AuthData (i.e. one that doesn't match authConfig.AuthData) is passed to aggregatorRoute and friends, a compilation error results.

As a bonus, the signatures of the user-facing methods are much simpler.

Needs a version bump before merging.

[rwalbergpd]

This makes more sense. Thanks!