Fix project name in file preambles
Add test_db_connection to InitDB and DropDB
Add __future__ imports and remove unused imports
Catch ConfigError in PrintingService
Assorted cosmetic fixes
Remove testimonials from README

The list was growing long and having it only on the website avoids
synchronization issues and improves graphical presentation.
Add some instructions to the README

Like a link to the homepage and instruction on how to download the
stable version and where to open bug reports.
Add commenting feature

Admins can internally comment submissions (OK, strange bug,
interesting, grading failure?, ...).