Added getIlluminationDirection for line scanners (#259)

* Added getIlluminationDirection

* Added getSunVelocities

* Adjusted conditional statements to better meet internal conventions.

* Factored getSunPosition into its own function.

* Changed vector lengths from shorts to ints

Images could have tens of thousands of positions and/or velocities and shorts cannot hold that many, so they need to be ints.

Co-authored-by: Jesse Mapel <jam826@nau.edu>