added formatted_event_date_range

it's a little overcomplicated to support my understanding of
french.  Do we support french?  no.  But the fact that
we've used internationalizable dates so far made
me not want to break convention.
more idiomatic factories, randomized event number of sessions
Install latest PhantomJS with every testrun so Travis CI fails less
Merge pull request #117 from tjgrathwell/try-to-fix-travis-ci

Install latest PhantomJS with every testrun so Travis CI fails less
Attempt to de-flake event volunteer request spec by waiting more