Prep for clustering functionality

[technige]

The prep work for clustering (primarily refactoring) moved into a separate PR for clarity. This includes:

• Relegated Config class to surface-level helper only. Separate "settings" classes have now been added to manage separation of concerns and management of defaults more sensibly. Significant new classes here are ConnectionSettings, SecurityPlan and PoolSettings.
• Cleaned up usage of URI vs address (host:port pair). This includes more clarity around the bolt scheme to describe current behaviour as opposed to future behaviours, such as discovery. The class InternalDriver class is now called DirectDriver as we will end up with multiple Driver implementations.
• Refactored much of the TLS code to work better with the separate SecurityPlan class. This means that some of the behaviour that was previously executed lazily (such as validating certificates) is now done eagerly and will therefore fail sooner on error.
• Tidied up format of log messages to make consistent with other drivers.
• Some package renaming and restructuring to better reflect the organisation of the code.