updated MP javascript source

As listed here :
https://groups.google.com/forum/?fromgroups#!topic/mp-dev/MzafgihlBwU

And as listed here: https://mixpanel.com/help/reference/javascript
Tracking all pageviews as one event, with different properties

Tracking individual pages as individual events is a recipe for disaster
in terms of being able to process the data in MP, and is not how they
recommend things anyway.

See https://mixpanel.com/help/reference

https://mixpanel.com/help/questions/articles/why-measure-events-vs-page-
views
Set some properties for ourselves that I think are important

registering some properties for the invididual that I think are
important to our business.
WP version stuff updated