Update RoR curriculum outline

Implements changes from the basecamp discussion at https://basecamp.com/1940253/projects/3866233/messages/32978315

Some general questions (that may or may not block this PR):
* Any thoughts on the language around the design section? Should it be removed entirely?
* There are a lot more JS-related bullet points here than Ruby related, which isn't necessarily a problem, but does seem a bit odd. Is that potentially confusing to people debating between FEE and Rails? Are we leaving out any Ruby-land tools that deserve a mention?
* Oxford commas - how do people feel about them?