Rewrite watchpoints to be much more stable

Rewrite watchpoints to be much more stable

This mainly involves a separate abstraction layer for elements (e.g. $a->b) and watchpoints (on pointer of the Bucket for example).
Also better comparison handling (value backup vs. page dumps).

It is not yet finished (there are sometimes false positives announced and names not yet perfect), but the functionality is working and not crashing as far as I have tested.
Future scope is also relative watchpoints, e.g. "w $this->val expression()" which does not have the symbol tables as basis, but the value (in this example: return value of expression()) as basis.