Progress Bar now updates upon returning

The progress bar had the problem that it wasn't updating
when you returned to the mainActivity. This was solved by
implementing the onResume() method and updating the
progress bar from there upon return.

-implement the onResume() in mainActivity in order to update
the progress bar correctly
-implement a method for updating the progress bar in the main
activity and put it in a separate method
-make the progress bar compeletely green once the budget is