[PE-295] Rationalise Gemfiles across all projects. All gem versions should be roughly the same

All gem versions should be the same across all projects now.

The main changes are anchoring Capybara at 2.1, for Ruby 1.9.3 compatibility, and Sinatra at 1.3.6. Sinatra is held at this version across all projects due to the `sinatra-r18n` dependency introduced by RubyCAS server. Some gems that get pulled in as dependencies that were explicitly included have been removed.