Various fixes

• Added option 'Break on Interrupt' in vscode's BREAKPOINTS panel. Therefore the command "-e breakinterrupt on" has been removed.
• Added missing config attributes for "z88dkv2".
• Changed "z88dkv2" parser to understand both, 4 and 6 digit addresses.
• Fixed a problem with disconnecting/reconnecting the ZX Next.
• "-dbg" debug console command added to help finding the root cause of 'unverified breakpoint' errors.
• Fixed 'step-back' in unit tests.