Add ga() options option to trackVirtualPageview

This allows options like hitCallback to be specified for virtual
pageviews.
Send a virtual pageview on manuscript upload

This is required to create a goal funnel in GA, as you can't create
a goal funnel from a non location based goal.
Merge pull request #284 from ucamhal/avocet/ga-manuscript-funnel

Track end of manuscript submission with a virtual pageview