Fixes

- Added titles to essays and questions
- Default titles for solutions and essays ( "Sample essay for {title.question} by {essay.user}" and "Feedback on {title.essay}" if title is blank)
- Batch update or create questions with CSV file. Visit /batch_update/questions to do that. 
  If "Allow create" is checked it would try to find and update questions first and create if it doesn't exist.
  If not then it will complain if the question doesn't exist.
  It displays only the first error even if there are multiple of the just for simplicity.
- Slugs for questions, essays, solutions, users.