Timestamp sensor data

Add a timestamp (can be as simple as a timer count) to each group of data for each sensor (i.e. the accelerometer measurements from an IMU should have a different timestamp than the magnetometer measurements from the same IMU). You will have to add variables in structs for this. Keep the naming conventions consistent and put the timestamps in the same hierarchy as the data it is stamping. Also please clearly label the conversion between the timestamp value and seconds (or milliseconds) somewhere visible in the code.