Use track probabilities from feature tracker

[plusk01]

• Modified OpenCV cv::goodFeaturesToTrack to return detection scores (see opencv-gftt-scores)
• the scores are converted to "probability of being tracked" by normalizing the scores using the max features score
• feature_tracker publishes probabilities in one of the PointCloud message channels
• the feature_selector uses them
• probs are removed from the image_t data structure before giving them to the vins_estimator (gross)