Implement figureOutBudgetStartEnd method

This method will figure out the start and end dates of the budget
according to the logic implemented.

-Figure out budget start and end dates according to the special logic and
put the values in SharedPrefs.
Modify and use getExpenseBetweenStartEndDates()

-Modify getExpensesBetweenStartEndDates method to use the budget start and
end dates that were saved in the figureOutBudgetStartEnd() method in
ProgressFragment.
-Refactor other methods in ExpensesDataSource to use the same columns
everywhere to avoid confusion.
-Use the getExpensesBetweenStartEndDates in the ProgressFragment to update
progress bars.