Feature/db

- Created bunch of classes for Database.
- ExpenseTable is now the way to save data.
Only functionality in ExpenseTable that is left is to update existing Expense Item.

@KevinTse you can merge this pull request.
I've changed the manifest's launcher to point to the TestDbActivity.
After merge, you can switch back to Main.

You can modify your Money Manager to save to the ExpenseTable instead now.
Example code is in TestDbActivity.