Class Time

* This singleton class represents the current simulation time in OpenSpace. It internally * stores the time and provides methods to set the time directly (setTime(double), * setTime(std::string)) using a `double` value using the number of seconds passed since * the J2000 epoch or a `string` that denotes a valid date string in accordance to the * SPICE library (http://naif.jpl.nasa.gov/pub/naif