Enhanced test flow

Added test status flag for easier checking of a test's status;
Adapted the tests index page to reflect this change.
Implemented basic score management

Stored answers in session and computed them in result view;
Wrote the result view with basic flow security and basic score management;
Added the result.html template.
Fixed session bug

Fixed a bug which occured when consequently giving up a test before starting a new one.
Added description to test list on index page