Add verbosity flag to optionally prevent excessive std::cout writes

[ahrnbom]

Since DLIO writes directly to std::cout, as opposed to using ROS' output system (ROS_INFO etc.) it's difficult to control the amount of terminal output you get. For example, it was quite difficult for me to read the estimated attitudes and biases, as this got overwritten by the info box. This PR adds a verbosity flag which removes the info box from the terminal output, if set to false.