Deleted monthly overdraft, formatted the numbers

Removed the monthly budget overdraft functionality for now as it will take
another weeks to implement it correctly and I don't have this time right
now, so it'll have to wait till the next version.

- delete everything related to monthly budget overdraft functionality
- format the numbers accordingly in Progress and Expenses Fragments, so
  that they have thousand separators, which make it better for visual
  comprehension.