Bug 935636 - Avoid duplicating data on contact merge

Ok, if it's too hard let me follow this code for you:
What we want to achieve here is not merging anything if source & destination objects are the same. The easiest way to compare two objects is to compare their stringified values, when we don't need to do deep loop with checking every value in source against every value in destination objects. We just check JSONs of the objects so we will know if the are equal or not....