Made some small changes to Flight (just the toString()), Payment, and
Receipt in order to make the receipt print out more clearly and easier
to read on the ReceiptScreen.

Also modified FlightScreen.java to try to implement the case when no
search criteria is entered resulting in all flights from the entire
database being printed.

I was able to modify the code easily except for I didn't know how to
actually print out all the database flights. I tried flightL.toString()
(which I have in the code currently), but that didn't work, so if anyone
else can figure it out, please fix it!!!

I have made a comment in FlightScreen.java which line of code needs to
be fixed so it should be easy to find/locate in the file!

Also, if anyone can find a quick fix for the prices not showing two
digits after the decimal place, fix that as well please!!!