Feature 137 - mongoose history

Added ability to use mongoose history (https://github.com/rossan/mongoose-history).  There is an option named saveHistory that defaults to false meaning no history will be saved on the list.  There are a few concerns i have and they are as follows:

1. I added a conditional statement in list.js within the constructor to check if option saveHistory === true then use mongoose-history plugin for that list, however, there probably is a more elegant way to accomplish this same task, but I could not find where you enforce options on the list.

I also updated the docs with the new option and information needed to use the history option
Determines whether or not the item's state is history is saved

Should it be

Determines whether or not the item's state history is saved?