Syntax highlighting of Solutions pages

Merge branch 'release/2.0.0-alpha4'

Merge branch 'release/2.0.0-alpha3'

Merge commit '8a9f2f8a0a7683fa0bad8bf33f209cb915e2ce3c'

Update to clojure 1.4

Switch to refheap for pasting.

Try to recover from OOM issues

Whole buncha new stuff.

Put session data in mongodb

Fix problem submission, static URLs, invalid dependencies