[course stats] better ui and leikkaavuus tweaks

[mluukkai]

• Show all the course names when leikkaavuus is applied:

• Display course codes and course names clearer and in larger font, also display names of the substituting courses
• Examine possibility to exclude certain substituted courses after fetching the stats
• Examine "symmetric substitutions" meaning that substitution would only be included if the other course has the first course in its substitutions, maybe should be done in updater