Extended support for checklist

Now it's possible to specify the minimum number of choices selected
before proceding to the next question
Small fixes

- extended support for headers without answers
- moved the column indexes to constants, so that it's easier to work
with changing excel sheet forms
- extended debugging for input files (doesn't break at first error,
reads all questions and reports types of bugs)
- added new questions to the survey
Bugfixes

- Corrected the bug with the wrong progress estimation and added
support for steps of less than 1% (important for forms longer than 100
questions)
- now choosing a radio answer is enough to continue, without having to
click the "next" button
bugfixes

- added one click advance to scale and list questions
- fixed formatting of scale question
Merge branch 'master' into production_sensibledtu1k