[SPR-8387] Introduced supports(MergedContextConfiguration) method in the SmartContextLoader SPI; updated existing loaders accordingly; and fleshed out implementation of and tests for the new DelegatingSmartContextLoader.

[SPR-8386] Completed JavaDoc for AnnotationConfigContextLoader regarding the SmartContextLoader SPI.

[SPR-8386] AbstractContextLoader now adheres to the SmartContextLoader contract by verifying the existence of generated default resource locations.

[SPR-8395][SPR-8386] AnnotationConfigContextLoader now generates a list of default configuration classes by finding all non-private, non-final, static, inner classes of the test class that are annotated with @Configuration; updated JavaDoc in AbstractGenericContextLoader and AnnotationConfigContextLoader to reflect changes resulting from the SmartContextLoader integration.

[SPR-8386] Polishing SmartContextLoader SPI; AnnotationConfigContextLoader now only considers static inner classes annotated with @Configuration as configuration classes.

- introduced processContextConfigurationAttributes() method in SmartContextLoader SPI
- refactored AnnotationConfigContextLoader, AbstractContextLoader, AbstractGenericContextLoader, ContextLoaderUtils, and TestContext implementations to take advantage of the SmartContextLoader SPI, MergedContextConfiguration, and ContextConfigurationAttributes
- deleted ResourceTypeAwareContextLoader
- deleted ContextLoaderUtils.LocationsResolver and implementations
- moved context key generation from TestContext to MergedContextConfiguration

[SPR-6184] AnnotationConfigContextLoader now defines "$ContextConfiguration" as the resource suffix for generated default @Configuration class names.

- Removed AbstractGenericContextLoader's createGenericApplicationContext() method.
- AnnotationConfigContextLoader now uses an AnnotatedBeanDefinitionReader instead of working with an AnnotationConfigApplicationContext.
- AnnotationConfigContextLoader now uses the supplied GenericApplicationContext to load configuration classes.

[SPR-6184] completed JavaDoc for AnnotationConfigContextLoader; polished JavaDoc for other concrete context loaders.

[SPR-6184] Introduced ResourceTypeAwareContextLoader interface and removed dependency on AnnotationConfigContextLoader in TestContext.

[SPR-6184] AnnotationConfigContextLoader now generates a default configuration class name; fleshed out documentation of AnnotationConfigContextLoader; introduced sub-package and suite for configuration class tests.

[SPR-6184] AnnotationConfigContextLoader now calls AnnotationConfigApplicationContext's register(Class<?>...) method in one go, via var-args.

[SPR-6184] AnnotationConfigContextLoader now extends AbstractGenericContextLoader; added new extension points to AbstractGenericContextLoader.