Rework DjangoStaticFileHandler (fixes #1034)

Fixes multiple issues
 - Unicode errors when path contained non-ascii characters

 - 403 errors when the current working directory was not a parent
   directory of the static files

 - "API abuse" super() implementation of the get() method was passed a
   filesystem path instead of the url-path it was expecting

 - The above could also lead to 403 errors on case-insensitive file
   systems due to the way the base-class resolved and validated paths
   with respect to self.root
Merge pull request #1054 from andkit/fix-1034

Fix unicode errors when getting static files (fixes #1034)
fix #1044 Remove GNU GPL header
Fixed #947: Move pdf functions of participant app to new pdf.py
Fixed #1070 (Clear search index for deletedb and syncdb command)
Make sure QuestionView.get_question_message is in a unicode context.

This is important if the attribute question_message is set with
ugettext_lazy which needs an unicode context

Fixes #1066
Merge pull request #1062 from DerPate/fix#1044

Fix#1044
Merge pull request #1064 from emanuelschuetze/fix-947

Fixed #947: Move pdf functions of participant app to new pdf.py
Merge pull request #1069 from ostcar/reset_passwort_question

Make sure QuestionView.get_question_message is in a unicode context.
Use the default django message back end
Merge pull request #1060 from ostcar/use_default_message_backend

Use the default django message back end
Merge pull request #1071 from emanuelschuetze/fix-1070

Fixed #1070 (Clear search index for deletedb and syncdb command)