GsonBuilderUtils for programmatic Base64 serialization setup; common Base64Utils class adapts between Java 8 and Commons Codec

Issue: SPR-9488
Support Groovy Markup templating in Spring MVC

This commit adds support for Groovy templating, available as of
Groovy 2.3.0 (and 2.3.1 for advanced use cases, such as layouts and
fragments).

To enable this, one should create a new GroovyMarkupViewResolver
Bean in her application.

Issue: SPR-11789
Refactoring : work in progress