add possibility to set the income

[BuZZ-dEE]

add possibility to set the income

[DennisBauer]

@BuZZ-dEE thanks for submitting a feature request!
Can you please add some more details on how you could image this to work and look? How would you prefer this to be shown? Adding this as a feature I would definitely do it as an optional way of using the app not do this by default.
Also take a look at #48 where this was already mentioned by @domportera, who achieved the same by adding the income as a negative expense.