Added ApproximateDateField to model and updated initial data fixture.

Created two new fields in the person model to hold the persons approximate birth and approximate death. Updated the initial data fixture to include the approximate birth and death  year, month and  day.
Altered views to include approximate date.

Changed the people_view and person_detail template to include approximate date instead of the birth and death year. Updated the model string method to include the approximate birth and death dates and updated the person model test to match the model string method.
Altered views to include approximate date.

Changed the people_view and person_detail template to include approximate date instead of the birth and death year. Updated the model string method to include the approximate birth and death dates and updated the person model test to match the model string method.
Merge pull request #11 from jzmiller1/ADate_fb

Added ApproximateDateField to model and updated initial data fixture.