Kalman estimator overloaded with 4 base stations

[krichardsson]

When using 4 lighthouse V2 base stations and all of them are received at the same time, the kalman estimator has a hard time processing all the data. The symptom is the "ESTKALMAN: WARNING: Kalman prediction rate low (98)" warning in the console log.

Each base station produces 50 x 2 = 100 sweeps / second.
4 base stations have 100 x 4 = 400 sweeps / second
There are 4 sensors on the deck ==> 400 x 4 = 1600 sweeps pushed to the kalman estimator every second.

The suggested solution is to add a throttling functionality that discards measurements in a structured way to keep the system load at acceptable levels.

[krichardsson]

Implemented in #1117 but there still seems to be some problems and warnings.