Removing null from Kea JSON syntax
The JSON standard allows a null entry but:
- it is not used at all in Kea and as now we are in version 2 we can expect it shall be never used
- there is a possible confusion between a null Element shared pointer and an Element shared pointer pointing to the null Element
So I propose to remove it from syntax, element type and all tools using JSON and/or Element objects and shared pointers.