Refactored exam protocol renderers
The new code reduces the sinze of inclass-exam.wf significantly by
moving the exam protocol into test-item-procs.tcl. In the same step,
the largish function was split up, the rendering functions of
submissions are now named consistently, and there are now different
functions for rendering single items vs. many items, making the
single-item rendering reusable. Additionally, the answer manager is
documented in a more eye-friendly and modular way.