QTI 2.1: add information about converting

If a test or questions are converted, a wizard appears. In the wizard an text about converting should appear, as well as the link to to manual.

• when converting test in the learning resource test
• when converting questions in the question bank

use the following link: https://confluence.openolat.org/display/OO113EN/Change+from+QTI+1.2+to+QTI+2.1