All courses: Remove texts referencing to "exercise x"

[jeeemil]

Courses

This issue is actually related to all courses, but I would suggest that we start with the most common QGIS courses.

Description
When creating tailored courses with CourseCrafter, there's often an issue that the exercise materials mention the exercise number

For example "tallenna se nimellä “QGIS-harjoitus 2”. This is a problem when you do a tailored course, because the exercise number might be something else. At the same we should check that there are no mentions in the body text like "As we did earlier in exercise 2", because these need to be corrected each time for each tailored course. In order to cut down the time it takes to prepare tailored courses I suggest the following changes.

Solution
Go through the texts in each exercise and change all mentions of exercise numbers to something else that's not referring to a certain number.
"tallenna se nimellä “QGIS-harjoitus 2” could be "tallenna se hyvällä nimellä” or something.

This is issue could be useful to split it up for each course.