Create visualization for Kalman Filter Gain

[connor-wool]

While the Kalman Filter is an important part of our localization system, and the data it provides is used to modify the particle filter, we don't actually know what it's internal state is at runtime.

Completing this will require a couple things be completed. Trivially, a ROS publisher will have to be created within the Kalman Filter class, and then the Kalman filter will need to publish it's internal state on this topic each time it is called upon by the particle filter.

Ideally, we can do this without overly increasing the latency of the system.

Finally, an RQt plugin will need to be built which consumes data from these topics, in order to visualize what the state of the Kalman filter is (and how it compares to the particle filter)