ISPN-3252 Migrated Configuration API in Spring module

* Moved the GlobalConfigurationOverrides class to it's own file. This was just for consistency with ConfigurationOverrides which was already on a separate file. The alternative was to have ConfigurationOverrides as a sub-class as well, but that would have just made for too much noise.

* Updated Javadocs in AbstractEmbeddedCacheManagerFactory. Removed references to org.infinispan.config.GlobalConfig and pointed to relevant methods in org.infinispan.configuration.global.ConfigurationBuilder

* Removed any API relating to CacheLoaderManagerConfig. The rest of the clean-up for that class will be made in a separate JIRA (probably).

* The internal call for rehashWaitTime was commented as 'no longer used' - hence the public API for that on Abstract EmbeddedCacheManagerFactory was removed.

* AbstractEmbeddedCacheManagerFactory#setCustomInterceptors() took in a List<org.infinispan.config.CustomInterceptorConfig> and that was changed to take in a List<? extends CommandInterceptor> so that they could be added to the interceptor chain individually using a CustomInterceptorConfigurationBuilder.