WINTERMUTE: Use a pointer as temp when building ScWatch.

Otherwise the destroyer for ScWatch will be called at the end of addWatch,
which e.g. calls delete _lastValue, which is premature.
WINTERMUTE: Add removeWatchpoint to script engine, for debugger support.
WINTERMUTE: Fix typos/nonsensical code in getWatchlist()

Previous code referred to _breakpoints instead of _watchlist, clearly nonsensical.
Also tried to access array at size().
WINTERMUTE: Remove delete _lastValue from ScWatch destructor, it being non-exclusive.
WINTERMUTE: Add delw command in debugger to remove watchpoint
WINTERMUTE: Remove & rename duplicate watch-related debugger internals