Add commands to reset to defaults.

[MuppetGate]

To prevent the workflow becoming unusable through dodgy settings, it might be a good idea to add a couple of commands to set the defaults

dcalcset reset defaults will set the date/time formats back to their default settings.

decalcset reset anniversaries will delete all anniversaries and reset to the default entries.

Yes, the commands are long, but that should stop folk from tripping them by accident.