Reposition test, development group

Develop seems to be a debugging group so should
take lowest visual precedence.
Move gems to appropriate Gemfile Groups

Don't install things we don't need in the given environment.

Mainly an attempt to speed up CI builds somewhat:
http://docs.travis-ci.com/user/languages/ruby/#Speed-up-your-build-by-excluding-non-essential-dependencies
Rename develop Gemfile group to debug

Develop is too similar to development to mean anything different.
Don't install debug gems for CI
Merge branch 'update_gemfile' into rails-3-develop