GP001: fix outdated filenames in exercises

[eemilhaa]

Fixes #45

In addition to just replacing file extension, I also updated the filenames according to the new course directory.

Some things to consider before merging:

• Exercise 2: all shapefile-specific explanatory text is now removed (dfc67f6), leading to a lot of rewording in the exercise in general. This should probably be checked.
• Exercise 6: The metadata file for the population dataset Vaestotietoruudukko_2022 (in .pdf format) is missing from the data directory. External to this repo, but I'll still mention it here.
• All in-text references to the course directory expect the structure to be Kurssihakemisto/Harjoitus_x/some.file. The current course directory structure is simply Kurssihakemisto/some.file. I left the paths untouched based on 40 gp002 change all shp to gpkg #43 (comment)

[github-actions]

Preview changes here.

[jeeemil]

Elisa is in charge of this course, but since she is away, and I've been teaching this course in the spring at least once I guess I could check the Shapefile-text. Since the data is changed the only logical thing to do is to also change the text as you did. I think we could go forward with this and when Elisa returns, or if the course is up for more in-depth updates, then it could be discussed if we should have an exercise where we go through shapefiles. Then we could just grab the nice tables and stuff from this course. In any case I feel the most logical data to add in the beginning would be a geopackage so a shapefile-add could then be a completely separate topic.

I updated the course directory, so point 2 and 3 are done.

[github-actions]

Preview changes here.

[jeeemil]

@eemilhaa I updated a few images where the old files where present. If the changes are okay with you, this PR is ready for merge.

[eemilhaa]

@jeeemil Looks good to me, good catch on the screenshots!