Automation of end-date based on start-date

Hey,
@nursix Please Review
@flavour Removed the seperate js file and put in s3.datepicker.js
I'm still not convinced of the value of this deployment setting.

Imagine this setting in a web setup UI! Who is going to configure it? 

I think people will find it like a setting for the standard colour of snow, and isn't it rather so that the validity periods of credentials typically average around a year, with some credentials (not deployments!!) having a longer, and some a shorter standard validity?

IMHO this should be a user-facing widget, where the user selects a start date and then, /instead/ of picking an end date, he selects an interval length from a drop down with one option being to choose a particular end-date. I've described this before.