Issue #11 : Date picker display state maintained between page reloads.

There's been a lot of reorganisation in the javascript code, which I hope you'll approve of.  An object "leo" has been used to create a namespace within the DOM to avoid collisions with other variables and functions.

The query string code is written to make manipulation of key/value pairs easier as well as the generation of query strings.

A query string is used to track if the date picker was opened or closed.