Fix the Add Purchase button

The first commit has a lot of comments in it that you'll want to remove.

The second commit is obnoxious to read. Better to just look at the overall project structure. Also the `.gitignore` file got the important changes.

The 3rd commit is the one w/ the code fix. Basically, I just broke the `BudgetFragment` into it's own class. This lets you encapsulate all the logic for that "screen" in there. The `MainActivity` only has the view paging logic.