Add calculations

Implement Calculator class into PrayerTimes 2.0.

Class Advantages:

1- Define prayers as objects with three characteristics:
    a) Name: an identifier that defines the prayer time
    b) Type: the type of time calculation ( the time the angle is exactly X, or the maximum
                 angle within a period of time)
    c) Angle: The angle at which the prayer occurs

2- Easily add more prayer times (just define object with a name, angle, and type)

3- Customizable prayer angle instead of the old hard-coded implementation.

4- Calculate the prayer times for a batch of Prayer objects at once.

5- More structured code that's easily maintainable and upgradable.