Clarify the use of sessionTransacted

This commit clarifies the role of the external transactionManager for
a DMLC and the relationship with the sessionTransacted flag

Issue: SPR-9200
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