SWSV: LAB2b simplified and redesigned

Based on the feedback from the first lab sesison, we simplified the and redesigned the 'Integration testing' part of LAB02.

The wiki page explains the application and the existing tests more clearly, and the exercises focus more on extending the existing functionality.

If you have previously completed the lab, then there is no further action required. However, if you have not started it yet, be sure to use the new version of both the code and the exercises.