[PLAT-6849] Added tests, simplified annuity builders

Conflicts:
	projects/OG-Analytics/src/main/java/com/opengamma/analytics/financial/instrument/annuity/AbstractAnnuityDefinitionBuilder.java
	projects/OG-Analytics/src/main/java/com/opengamma/analytics/financial/instrument/annuity/FloatingAnnuityDefinitionBuilder.java
	projects/OG-Analytics/src/test/java/com/opengamma/analytics/financial/instrument/annuity/FixedAnnuityDefinitionBuilderTest.java
	projects/OG-Analytics/src/test/java/com/opengamma/analytics/financial/instrument/annuity/FloatingAnnuityDefinitionBuilderTest.java