Continue to support spring.jpa.hibernate.namingstrategy

In 1.0, the property spring.jpa.hibernate.namingstrategy could be
used to configure Hibernate's naming strategy. This was at odds with
most other configuration where binding to namingStrategy would require
a property with some indication that it was two separate words, for
example: naming-strategy, naming_strategy, or namingStrategy

This commit adds a new setter, setNamingstrategy, to JpaProperties so
that an app that was using namingstrategy in 1.0 continues to work
in 1.1.

Issue #928