Code review comment for lp:~vlewis/boots/vdev

Merged.

A couple comments:

* The default config options disabled this feature! I've modified them so the user gets 100 lines of persistent history by default, saved at ~/.boots_history.

* Whenever possible, try to keep UI-specific code out of the Console. I moved the save/load calls to inside the Plain UI class, and created a general "unload" method which, when called by the quitting Console, calls save_history.