Create DatabaseMaintainer class and methods

[tylermarton]

Create a class to be used for maintaining post data in our databases.

This also necessitates creating a Data interface class that UserData and PostData implement. The data class will contain an id attribute.

Create a method that will check UserData and PostData databases to ensure there is no data with duplicate ids. If there are duplicates, remove the most recent duplicate. The method will compare the id of Data objects, so it can be applied to UserData, PostData, and any other data objects that we create in the future.

[guanguangua]

200 pts