Update Dependencies/Gems

[squidgetx]

• We should be using spring, as spork hasn't been maintained in over 1 year and breaks in rspec 3.0.0
• FontAwesome 4
• Capybara 2.2
• CanCanCan
• Ruby-cas-client (cthielen has a rails 4 fork)

(Related to #535)

[mnquintana]

For future reference, there is a Gemnasium badge on the Readme that will show us when our dependencies get out of date. https://gemnasium.com/YaleSTC/reservations

[orenyk]

via #639, let's also make sure we're appropriately grouping our gems so that we don't load gems that won't be used in a specific environment.

[squidgetx]

Merging the upgrade-dependencies part into #774 and reorganizing into Rails 4 part 2 (#778)