Make the HikariModule a ConfigurableModule.

Supersedes #456.
Make it easier to use handlers/chain actions from the registry backing the chain.
Use Optional in the Registry API.
Allow InjectionHandler to inject optionals.
Ensure that JDK8u25 or higher is used if using Oracle's JDK
Revert "Ensure that JDK8u25 or higher is used if using Oracle's JDK"

This reverts commit 65aaf37a5a0fa1199bcd7e3540ece4d38ade6cef.
Pass the Subscription down the chain for the subscriber.
Build Pac4JCallbackHandler with a builder
Merge pull request #477 from tomdcc/pac4j-callback-handler-builder

Build Pac4JCallbackHandler with a builder
lambdas.
formatting.
Some reworking on the new Pac4J handler builder.

Generally simplified things, and removed docs that weren't quite helpful in order to push us to add docs that are helpful.
Add Tom Duncan as a contributor.