Add support for imaginary and complex numbers

[jsimonclark]

Add support for imaginary numbers (i.e. numbers that can be expressed as a real number multiplied by the imaginary unit i) and complex numbers (i.e. numbers that consist of both a real part and an imaginary part).

[jesper-friis]

The subclasses of NumericalData follows the classification of numbers in xsd (xml schema). Do we have a vocabulary defining data properties for complex and imaginary numbers?

[markdoerr]

@jsimonclark and @jesper-friis ,
due to the routes of EMMO in particle physics and quantum physics, I would even go a step further and add quaternions (in stead of only imaginary numbers) - Hamilton would be very delighted ;) - in case one really decides to go this route, one should not go it only one third. @jsimonclark , what do you plan to describe with imaginary numbers ?