Modified all necessary files to make the flight price print out properly
in the flight search screen as well as in the receipt screen (example:
$1300.00).

Also modified all necessary tests to get rid of all of the new errors
that came with doing the above so that all JUnit tests are successful.

Something to note is that the price of a flight is now a String but the
constructor still takes in a double for the price and then converts it
to a string internally!!!