udb - implement other udb time travel commands

See #190 

Implement these commands. Likely with the MI python classes.
```
> last [-f|-forward] [expression]
> ugo bookmark
> ugo start
> ugo end
> ugo redo
> ugo time
> ugo undo
> ugo wallclock
```

https://docs.undo.io/Commands.html#time-travel-commands
