Use Spring's method injection to set the dependencies for the message service

TODO: Ideally, we would be using Spring's method injection to set the dependencies for the message service.

File: /openmrs/api/src/main/java/org/openmrs/api/context/Context.java

CLASS: org.openmrs.api.context.Context

Line: 598
METHOD: private static MessageSender getMessageSender()

Line: 608
METHOD: private static MessagePreparator getMessagePreparator() throws MessageException;