Adding a show page and basic capybara tests

The total score needs to be displayed somewhere too,
probably in the last column of the table.
Adding a combined_score method for a level

This shows the score obtained for a level, independent
of the "total score" which is accumulated across all
the passed levels
Creates a source_code column and allows submission
Shows the source code nicely syntax highlighted
Merge pull request #13 from patrickdavey/with_source_code

With source code