better support for google analytics

[russ]

• track outgoing links
• track downloads and other clicks that wouldn't otherwise be tracked
• track ajax actions (e.g. viewing a note as a pop-up)
• include username/user role in tracking code

[russ]

i was going through GA capabilities recently, and realized this ticket was missing a number of good things...

[stoomey]

Russ says that 1) this might be one for Joe, except for the "include username/user role in tracking code", and 2) since this is a plos-specific task, and there's no GA in the ambra journals, maybe it should be a JO and not a trac ticket?

[stoomey]

Reassign to Joe since Russ indicated that there's probably some high-level, programmatic way to implement at least the first three bullet points.