Fix options shared state between instances of new Datamap()

[magic890]

The problem with the old line of code:

if (obj[prop] == null) obj[prop] = source[prop];

was that obj[prop] is a pointer to source[prop], this cause a shared state of memory between different instances of new Datamap().

Now it's fixed using a deep copy implemented in pure JavaScript (no additional dependencies! 🎉).

I've also tried jQuery.extend({}, ...) and _.cloneDeep but they had problems evaluating Datamap.prototype.draw on line var pathAndProjection = options.setProjection.apply(self, [options.element, options] );

This will close #296