vote to add mvc video

I'm suggesting adding an mvc video from youtube. It's something I use personally when teaching and there's a certain amount of authority and succinctness a video has over a text explanation.
added descriptive text to video expanation
link to Github Guides. Closes #349
Fix upvote_topic_path ref that was incorrectly stated as topic_upvote_path
Remove 'learn-to-code' step index in favor of declaring next_step in each file

Move learn-to-code images into an /img/ subdirectory
Add jQuery and CSS to titleizer for benefit of Frontend site
Serve up /:site/:subdir/:file.:ext paths directly from disk for all values of subdir

Previously this was only true if the subdir was /img/
Consolidate declaration of DOC_TYPES to a single list
Upgrade all Rails 4.0 refs to 4.1

Include big scary blue tip warning on the 'Create a Rails App' page
stating that rails 4+ is required
Set ruby to 2.1 in the Gemfile
Intermediate Curric: fix markdown fail in formatting of 'replies_controller'
Upgrade Sinatra to 1.4
Add .travis.yml to enhance working-ness of Travis build
Remove WORKSHOP.md readme file

It suggests that people commit back their changes to the
opening/closing presentations. Realistically, nobody ever
does that, which is fine.
Create job-board curriculum for begintermediate students

- Add discussion, error, and source_code_with_message methods
- Update docs index
Rename name-collisiony discussion method so that the intermediate curriculum isn't broken
Fix silly name clashing that ruined the intermediate curriculum CSS
Really kill Turbolinks and clean up mistakes

- Fewer syntax errors, more accurate instructions
Add Atom editor as an option

Apologies for being a tiny bit of a company shill here, but I wanted to add Atom because it's
1. free & open-source
2. hackable with HTML, CSS, and JavaScript, which might be cool for RailsBridge grads looking for challenges to apply their new skills to.
Typo fixes and add content to placeholders