Added a Authy Dashboard Widget

I have added an "Authy Dashboard Widget" that will show the Authy Statistics similar to the Authy Dashboard (http://dashboard.authy.com).

The number of months to show is configurable on the Authy Settings page, obviously if the user only has 3 months of stats and they enter a number higher, it will only display the 3 months (3 is the default).

There is also an option on the Authy Settings page to globaly enable or disable the Dashboard Widget.