A rough start on the 'learn' subsection
Getting homepage in line with wireframes

https://github.com/mozilla/CSOL-site/issues/116
Merge pull request #138 from andrewhayward/homepage

Merging homepage layout
Simplifying `learn` controller

Removing all references to models, etc.
Putting `program`s back for now
Fixing filter logic
Setting a default page title in 'Learn'
Adding the challenge thumbnail
Merge pull request #100 from andrewhayward/learn

Simplified this pull request greatly, so pushing it through to get more wireframes up.