Upgrade to Boot 1.1

This commit updates Sagan to use Spring Boot 1.1.

Sagan's direct use of Flyway has been removed in favour of using the
Flyway auto-configuration that was added in Boot 1.1. To limit the
required configuration the migration scripts have been moved to their
default location.

namingstrategy has been renamed to naming_strategy to allow it to bind
to the namingStrategy property. For consistency ddl-auto has been
renamed ddl_auto.