ACTS-345 Add Unit test for fit of perfect measurements

Fixes ACTS-345. I am trying to add some tests for the Fitter, for the bugs I fixed and to make sense of the lingering problems. The problem is that KalmanFilter is quite a complex class, which needs geometry, extrapolation, several helper classes. There is therefore some code duplication with the boilerplate code in the main example, and the FittingTest I'm trying to add to the Framework. @cgumpert Maybe it may be solved by adding some higher-level functions, or breaking some of the functionality into easier-to-test routines?