Gem upgrades

Next stop after Ruby 2.1: gem updates. This pull request upgrades all our gems to the newest version, with several exceptions:  

* rspec: there's a bit more to the RSpec 3 upgrade, I'll do that in a separate follow-up
* rails: Rails major version change, need I say more?
* flutie, jquery, jquery-ui: upgrading these breaks the UI

Test plan: this, more than the Ruby upgrade, carries risks that our incomplete test coverage could cause problems. I'll try to do some local testing this weekend and report on results if I can.