Write a console-based application to help air traffic control (ATC) monitor all domestic flights taking place during one day (00:00 – 23:59). The application must include the following features:
1.	Flight information is kept in a text file, using the format in the example below. When the program starts, flight information is read from the file [1p]. Each modification is persisted to the text file [1p].
2.	Add a new flight. Each flight has an identifier, a departure city and time, and an arrival city and time [1p]. Flight identifiers are unique; flight times are between 15 and 90 minutes; an airport can handle a single operation (departure or arrival) during each minute [1p].
3.	Delete a flight. The user provides the flight identifier. If it does not exist, an error message is displayed [1p].
4.	List the airports, in decreasing order of activity (number of departures and arrivals during the day) [1p].
5.	List the time intervals during which no flights are taking place, in decreasing order of length. [1.5p].
6.	The tracking radar suffers a failure. The backup radar can be used, but it can only track a single flight at a time. Determine the maximum number of flights that can proceed as planned. List them using the format below [1.5p]:
05:45 | 06:40 | RO650 | Cluj - Bucuresti

Non-functional requirements:
•	Implement an object-oriented, layered architecture solution using the Python language.
•	Provide specification and unit tests for Repository/Controller functions related with the second functionality. In case specification or tests are missing, the functionality is graded at 50%.

Observations!
•	The day starts at 00:00 and ends at 23:59.
•	Default 1p.

## TODO
-= Iteration 1 =-
1. Write the Flight class
    -> what are the attributes?
    -> ! use properties for each of them

2. Write a FlightTextRepo class
    -> read the flights on program start (__init__)
    # -> save the flights text file (def save_file(...))
    # -> write method add_flight

3. Write the FlightServices class
    -> get_all_flights() # return all flights from repo

4. Write the UI class
    -> write the __init__
    -> display the main menu:
            a. Display all flights
            x. Exit
    -> displays all flights at menu (a)

-= Iteration 2 =-
0. Create /tests directory and add PyUnit tests

1. Write FlightValidation class
    -> is_valid (return True iff flight is valid)

2. class FlightTextRepo
    -> write method add_flight
    -> save the flights text file (def save_file(...))

3. Write the FlightServices class
    -> get_all_flights() # return all flights from repo
    -> add_flight(...)

4. Write the UI class
    -> display the main menu:
            a. Display all flights
            b. Add flight
            x. Exit
    -> displays all flights at menu (a)
    -> read flight data -> save it via services/repo


















