make a mock ga function when in dev mode

and remove the ga undefined check from ga_track_event
make ga-tracked links respond to meta-click
fix View Source Files link behavior

expand gaTrackLink to allow delegating selectors
in addition to actual jquery objects
follow clicks even when ga is inaccessible
Merge pull request #4909 from dimagi/gaTrackLink-rebase

Make ga-tracked links respond to meta-click