Implement Diceware Passphrase Generator

Note: This is a first swing. I do not have the hardware necessary to test it properly at the moment.

Fixes #163 
I think this method for generating indexes is incorrect. The method of looking of words based on dice rolls is for manual generation of passwords. Since we're using a flat array of 7776 elements, it's better to just do

    index = this.random(0, this.wordlist.length);