- allocate IMU and output buffers on construction according to defaults
- determine buffer max time delay based on configuration parameters
- reorder flowSample and extVisionSample to minimize padding
- adjust parameter defaults to match PX4-Autopilot
* Support vision velocity expressed in body frame
* Use switch statement for vision velocity frame
* Robustify vision velocity frame test
* Increase lower bound on vision velocity noise to 0.05 m/s
