Created initial models, tests and initial_data fixture.

Created initial implementation of Cemetery, Marker, Person and MarkerImage models to hold the data for the project and registered them in the admin. Each model (except MarkerImage) has a test for the __str__ method. An initial_data (JSON) fixture containing one Cemetery, five Markers and eight Persons was also created but does not yet contain MarkerImage data.  Models do not contain any geographic data.  Geographic data will be implemented in the future.