handle watchpoint-trigger event

Start process, set watchpoint via debug console, continue (and have the variable be changed). Result:

GDB stops at the line that is responsible for the change (as expected) but a red popup is shown in the editor window:

Exception occured

and the debug console has a note

Not implemented stop reason (assuming exception): watchpoint-trigger

Please handle that gracefully ideally give a visual output of changed variable in the editor window).

While it is a "feature request" I'd consider that also a "bug" because cwatch is one of cobcd's functions. No need to rush this because it is only a UI issue - it still "works" (in this case the new value is shown in the debug console).

[The bigger feature request is to handle watch via the watch window but that's a bigger thing which should be done later.]