Clean up Spring MVC Test Framework code

 - Formatting
 - Suppress warnings
 - Remove unused imports
Support Groovy scripts in the TCF

 - Introduced getResourceSuffixes() in AbstractContextLoader in order
   to support multiple resource suffixes in the default detection
   process. This feature is used by the new Groovy/Xml context loaders.

 - Introduced GenericGroovyXmlContextLoader and
   GenericGroovyXmlWebContextLoader which support both Groovy scripts
   and XML config files for loading bean definitions. Furthermore,
   these loaders support "-context.xml" and "Context.groovy" as
   resource suffixes when detecting defaults. Note that a default XML
   config file will be detected before a default Groovy script.

 - DelegatingSmartContextLoader and WebDelegatingSmartContextLoader now
   use reflection to choose between using GenericGroovyXmlContextLoader
   and GenericGroovyXmlWebContextLoader vs. GenericXmlContextLoader and
   GenericXmlWebContextLoader as their XML loaders, depending on whether
   or not Groovy and spring-beans-groovy are on the classpath.

 - Groovy scripts can be configured via the 'locations' or 'value'
   attributes of @ContextConfiguration and can be mixed seamlessly with
   XML config files.

Issue: SPR-11233