Test death before birth

1.) Add DeathBeforeBirth.java to contain all methods and logic to handle the death before birth errors. Most of the methods deal with formatting dates. getDeathBeforeBirthErrors is the main method which returns and ArrayList of Person objects that have death before birth errors.
2.) Add printDeathBeforeBirthErrors method to OutputDisplayer.java to call on getDeathBeforeBirthErrors method and retrieve the error results for output. 
3.) Capitalize lowercase "Sep" for @I2@ to make uppercase months consistent throughout the Gedcom file.
4.) Add DeathBeforeBirthTest.java to contain logic for tests. TODO: complete coding of robust test methods.