Models for M350+DJI controller

[03alebassi-debug]

• Implemented the DiscreteTF class, which takes the parameters of a discrete transfer function sampled at 50 Hz (simulation frequency) as input and computes the discrete update. The class is generic and supports transfer functions of any order.

• Implemented a specific model + controller for each axis, along with an additional attitude controller.

[KKalem]

• X,Y,Z controllers do not match their definition in Unity, use "forward, left, up" wording instead to avoid confusion.
• These 3 are nearly identical except the numbers... please merge "X,Y" into one "horizontal controller" and rename "Z" into "altitude controller".
  • Use some prefix to differentiate these from the generic ones. "Sysid_horizontal_controller" or sth is ok.
• I also would like to avoid future questions of "how can i use this for my other robot", so place all this under DJI instead, right next to "DJIController.cs".
  • The ultimate goal is to replace the horizontal, altitude and attitude controller scripts that the DJIController uses with these instead. So the more similar they are the better.
• Add a link to something that describes the parameters. b, aTail, invA0 etc are not at all things that can be modified without some text and math. A readme would do too.

[KKalem]

Couple little things here and there, but I'll fix'em up later. just some housekeeping.