Add EKF

[mollocon44]

Introduced:

• Jacobian functions for state and output equations in Model.h
• Matrix constructor from DynamicArray
• Elementwise operations (add/subtract/divide) in DynamicArray class

EKF files have been created and mutilated, but don't make a ton of sense just yet.

[teubert]

Thanks @mollocon44 , this is great!

One thing: Could you move inc/ExtendedKalmanFilter to inc/Observers/ExtendedKalmanFilter?

@jason-watkins and I will review the rest of the changes and make comments