Introduce new @Conditional annotation that can be used to filter
which @Configuration classes or methods are loaded. @Conditional
can be used directly or as a meta-annotation. Condition implementations
are provided via the 'Condition' interface and are free to filter based
on any criteria available at the time that they run. The
ConditionalContext provides access to the BeanDefinitionRegistry,
Environment and ConfigurableListableBeanFactory along with a
ResourceLoader and ClassLoader.

The existing @Profile annotation has been refactored as a @Conditional
with the added benefit that it can now be used as a method level
annotation.